javascript

JavaScript is a Scripting Language

A scripting language is a lightweight programming language.

JavaScript is programming code that can be inserted into HTML pages.

Scripts in HTML must be inserted between tags.

Scripts can be put in the and in the section of an HTML page.

How to use in body :-

.
.

.
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Document.write ka matlab hai ki html page mein kuch bhi likhna .

Javascript in head:-

My Web Page

A Paragraph

Javascript in body:-

My Web Page

A Paragraph

Button jispar click karney se alert box khuley :-

The alert() function is not much used in JavaScript, but it is often quite handy for trying out code.
The onclick event is only one of the many HTML events you will learn about in this tutorial.

My First JavaScript

JavaScript can change the content of an HTML element.

Output:

My First JavaScript

JavaScript can change the content of an HTML element.

Ek button

Jis par click karney se text chage ho jayega aur ban jayega hello javascript

Another example:-

src="pic_bulboff.gif" width="100" height="180">

Click the light bulb to turn on/off the light

Output –

Ek bulb hai jis par click karney se pics change hoti hai ……server got 2 pics one bulb on wali and off wali

Example :-

My First JavaScript

Please input a number.

Output:-

Ek input text area hhai aur sath mein ek button click karney par batata hai agar hum ismey abcd likhdey …..alert box khulkey batata hai .

Javascript :-

Create a variable called myName and set it to a string containing your name. Then type myName and press Enter to see what the variable myName stores.

var myName="viveck"

   myName

=> 'viveck'

Replace the blanks with the correct variable names in the following code: "My name is " + ____ + " and I am learning " + ____;

"My name is " + myName + " and I am learning " + favoriteLanguage;

'My name is viveck and I am learning JavaScript'

'My name is viveck and I am learning JavaScript'

Try creating a variable called myAge that stores your age. Then type myAge and press Enter to see its value.

myAge=23;

=> 23

Try setting myAge to a string that spells out your current age.

  myAge="twenty two";

=> 'twenty two'

Try checking if the variables alicesAge and bobsAge have the same values using the equality operator.

alicesAge == bobsAge

=> false

That returned false because Alice is 19 and Bob is 20. If they were the same age, your code would have evaluated to true. We've covered a few operators already, but check out some other commonly used operators in the description.

We've seen that variables have values, but did you know they also have types? The type of a variable is essentially the data type (e.g. string, number, etc.) that the variable stores. So how do we know if a variable stores a number or a string? We can use the handy typeof operator to figure it out. We've created a variable for you called secret that contains -- you guessed it -- a secret value. Can you figure out its type? Give it a try!

   typeof  secret

=> 'number'

Empty Cans, Empty Variables

Sometimes you might want to create a variable for later use, but don't know the value you want to assign to it just yet. JS lets you declare variables without assigning a specific value. In this case, the variable will have an "undefined" value. You can do this by declaring a variable and leaving out the assignment operator and any value. Try creating an undefined variable called emptyCan. Then check the type of the variable using the appropriate operator.

typeof emptyCan;

=> 'undefined'

Now that you have an empty variable, you can assign a value to it later.

Increment Operator

Now you know how to create and change variables. A common task in programming is incrementing the value of a variable, like we did when we increased the myAge variable by one. This is such a common task that there's a special operator for it in JS, the ++, or increment, operator. Increment the value of the variable called counter which we have already created for you. Then type the variable name counter and press Enter to see its updated value.

counter++;

=> 0

Awesome! The increment operator will be handy when you're writing a lot of code. There is also a similar decrement operator, --, which is used to decrease the value of a variable by one.

12Adding Numbers, Again

What if you wanted to increment the value of a variable by any number, not just one? There is a way to do this using the assignment operator. For example, if you want to increase the value of a variable x by 10, you can use the code x = x + 10;. 

This works because the code on the right hand side of the assignment operator is evaluated first, then the resulting value is assigned to the variable x. So JS evaluates x + 10 and then reassigns the result to the variable x.

Increment the value of the variable counter by 5.

counter=counter+5;

=> 6

You can also subtract any number from a variable similarly, by using the - operator instead of the + operator.

Another Addition Operator

Adding numbers to variables is such a common task in programming that there is a special operator for it. The += operator is short hand for incrementing a variable by a number. For example, instead of x = x + 10;, you can write x += 10;. They both do the same thing.

Use this operator to increment the variable counter by itself.

 counter += counter;

=> 42

Length of a String

Remember that a string is a sequence of characters. The length of a string is the number of characters in it. Every string in JS has a length property which stores the number of characters in the string. For example, "keep it up".length will evaluate to 10 (remember, spaces are characters too). 

Get the length of the string stored in the variable ls.

   ls.length;

=> 11

Selecting Characters    important 

Imagine that you have a list of strings containing words and you want to sort them alphabetically. You'll need a way to get the first character in each string. You might even need the second or third character if there are multiple words with the same first letter. 

The charAt(index) is a handy way to get the character at a specific position in a string. Keep in mind that strings are zero-indexed, meaning the first position is position 0, the next one is position 1, and the last one is position length - 1. 

For example, we can get the character at position 2 in the string "hello" by doing "hello".charAt(2). 

What is the last character in the string stored in the variable ls?

ls.charAt(ls.length - 1);

=> 't'

Good Job!

5Substrings

Easy hai samjho isko ab :-

Suppose ek string hai hamarey pass  “universityofengland” if u need the output of first 5 characters then we can use substring 

“universityofengland”.substring(0,4)  here o is starting index and 4 is end index……….. substring index from 0 remember and it wont include last string and gieves ur output first 5 characters 

Okk that’s it is easy

And this will return 

and "LearnStreet".substring(5); returns "Street"

to find character in a string :-

indexOf(value) returns the the first index of the specified character or string. 



Example: "LearnStreet".indexOf("e"); returns 1 because the letter 'e' first occurs at index 1.

It's great that we can get one character using charAt(index), but what if we wanted to get a longer part of a string? A contiguous part of a string is called a substring. The substring(start, end) function gives us a substring starting at the start index and going up to but not including the end index. 

Use the substring(start, end) function to select the first word in the string stored in the variable message. message stores the string "Hello World".

message.substring(0, 5);

=> 'Hello'

Change to Upper Case

It's time to get angry and yell at people on the Internet! Just joking ;) Instead of holding down the Shift key or using Caps Lock, let's try to code something to do it. We can use the toUpperCase() function to do this. 

Take the string message and return an upper case version of it. Update the message variable with the upper case version of it.

   message.toUpperCase();

=> 'I USED TO BE LOWERCASE BUT NOW I AM UPPERCASE'

What is your Index?

What if you wanted to check if a string contains a particular character or substring? One way to do this is using the indexOf(value) function. This function takes a character or string and returns the first index at which it occurs. For example, "the big bang".indexOf("big") returns 4 because "big" starts at index 4. When the character or string provided is not present, this function returns -1.

We received an email from an unknown source. The content of the email is stored in the variable message. The way our email application works is if the message contains the word "free", it goes to our spam folder. Find out if the message should go to our spam folder. If the email is spam (e.g. contains "free"), your expression should evaluate to true and otherwise evaluate to false.

   message.indexOf("free") != -1;

=> false

Nice! That should take care of most of the spam we get.

Reversing a String

Now that we've covered some commonly used string helper functions, let's try to do something a little harder. We're going to give you a string and you're going to return the reverse of the string. For example, if we give you "gum", you will return "mug". 

How do you do this? Remember that we can use the + operator to combine two strings together, and we can use the charAt(index) function to get the character at a given index. 

The variable message contains a three letter word. What is the reverse of the string stored in message?

   message.charAt(2) + message.charAt(1) + message.charAt(0)

=> 'hey'

What's the Secret?

Your friend wants to text you a secret message. But she doesn't want to send it in one text, in case your arch nemesis gets hold of your phone. Instead of just sending the secret message in one text, she's going to split up her secret and send you two messages. The first half of the first message combined with the second half of the second message will give you the full secret message.

The first message is stored in message1 and the second message in message2 Figure out what the full secret message is, using what you've learned so far.

   message1.substring(0, message1.length / 2) + message2.substring(message2.length / 2, message2.length) 

=> 'i ate your cookie'

*Write the function body below to return a string that is

      identical to str except that its first letter is capitalized.*/

    function capitalizeFirst(str) {

    return str.charAt(0).toUpperCase() + str.substring(1, str.length);

}

You're building a website and you want to store everyone's names with correct capitalization. People use all sorts of capitalizations when they enter their first and last name, like "jOhn SMIth", "anne doe", and "david Shi", for example. You want to store names so that only the first letter of the first name and first letter of the last name are capitalized, like "Amy Sue".

In the code editor, complete the function called capitalizeName that takes a string containing someone's full name, with their first name and last name separated by a space like "bOb dyLan", and returns the correctly capitalized name, like "Bob Dylan". We've already started it for you by converting the name to lower case. It will be useful to use the capitalizeFirst function which you coded in the previous exercise.

function capitalizeFirst(str) {
    return str.charAt(0).toUpperCase() + str.substring(1, str.length);
}

function capitalizeName(name){
    var lowerName = name.toLowerCase();

    var spaceIndex = lowerName.indexOf(' ');
    var first = lowerName.substring(0, spaceIndex)

     var last = lowerName.substring(spaceIndex + 1, lowerName.length);
    return capitalizeFirst(first) + ' ' + capitalizeFirst(last);
}

Let's do some more practice with functions. Write a function called square that takes a number and returns the square of that number.

function square(num) {
    return num * num;
}

Let's write a function that might be useful if you have geometry homework. Code a function called triangleArea that takes two numbers -- base and height -- and returns the area of a triangle with the given base and height. The formula for the area of a triangle is (1/2) * base * height.

function triangleArea(base, height) {
    return 0.5 * base * height;
}

Now we are going to code a function that says 'hello' to you. Code a function called hello that takes in one argument, your name, and returns the string "Hello, " followed by your name.

function hello(name) {
    return "Hello, " + name;
}

In this exercise, we won't be returning a value. We are instead modifying a global variable, x. Write the function incrementX that increments the variable x by amount.

var x = 10;

function incrementX(amount) {

 //Write code to increment x by amount. Don't return anything.

 function incrementX(amount) {

    x += amount;

}

}

Authenticate program:-

function authenticate(password) {

     var successMessage = "you are now logged in!";

     var failureMessage = "oops. try again.";

     if (password == "jsrocks") {

         return successMessage;

     } else {

         return failureMessage;

     }

}

Write a function called authChuckNorris that takes a username and a password and returns a success message only if the username is "chuck" and the password is "norris". Otherwise it returns an authentication failure message.

function authChuckNorris(username, password) {
    var successMessage = "welcome chuck norris!";
    var failureMessage = "sorry, try again.";

    if (username=="chuck" && password=="norris"){
        return successMessage;
}
    else{
        return failureMessage;
    }
}

Write a function named find42 that takes two numbers and returns true if either one is 42, their sum is 42, or their difference is 42. If any of those conditions hold, the function should return true. Otherwise it should return false. Remember that the difference of two numbers a and b can be a-b or b-a.

function find42(a, b) {
    return a==42 || b==42 || (a+b)==42 || (a-b)==42 || (b-a)==42
}

A palindrome is a word that reads the same forwards and backwards. For example, "civic" is a palindrome. Write a function called fivePalindrome that takes a string as an argument and checks if it is a 5 letter long palindrome. Return true if it is, and false if it isn't. First check if it is 5 letters long, and if it is, check if it's a palindrome. You can check if it's a palindrome by comparing the letters at positions 0 & 4 and 1 & 3.

Function fivePalindrome(word) {
    if (word.length == 5) {
      return word.charAt(0) == word.charAt(4) && word.charAt(1) == word.charAt(3);
    }else {
      return false;
    }
}

This is a slight modification of a popular programming interview question. Write a function called fizzBuzz that takes a number and does the following: if the number is a multiple of 3 but not 5, return "Fizz"; if the number is a multiple of 5 but not 3, return "Buzz"; and if the number is a multiple of both 3 and 5, return "FizzBuzz". If the number doesn't meet any of these conditions, just return the number itself. Use the isMultipleOf(firstNumber, secondNumber) function we've coded for you in the code editor to check if a number (firstNumber) is a multiple of another number (secondNumber). It returns true if it is a multiple, and false otherwise.

function isMultipleOf(firstNum, secondNum) {
     return firstNum % secondNum == 0;
}

function fizzBuzz(num) {
    if (isMultipleOf(num, 15)) {
         return "FizzBuzz";
     } else if (isMultipleOf(num, 5)) {
         return "Buzz";
     } else if (isMultipleOf(num, 3)) {
         return "Fizz";
     } else {
         return num;
     }
}

You don't like waking up every morning and thinking about how you're going to spend your day. As as result, you write a program that tells you what to do.

Write a function called decide that takes a string containing the day of the week and another string containing the weather, and returns a string telling you how to spend your day. If it is a weekday, return "go to work or school". If it's a weekend, check if it's "rainy" or if it is "sunny". If it's sunny, return "go outside" and it if it's raining, return "go code".

Use the isWeekday(day) function to check if it is a weekday or weekend.

function isWeekday(day) {
     return day == "Monday" || day == "Tuesday" || day == "Wednesday" || day == "Thursday" || day == "Friday";
}

function decide(day, weather) {

     var weekdayPlan = "go to school or work";
     var rainyWeekend = "go code";
     var sunnyWeekend = "go outside";

     //Complete the function body below to return an activity depending on the day and weather.
     if (isWeekday(day)) {
         return weekdayPlan;
     } else {
         if (weather == "sunny") {
             return sunnyWeekend;
         } else {
             return rainyWeekend;
         }
     }
}

•  

Arrays Introduction: An array is a datatype that can hold more than one value (known as elements) at the same time. This is especially useful if you want to group similar things together and go through them at the same time with a loop. You can think of an array like as a list of some objects, perhaps a shopping list and what you want to buy. An example would be: var shoppingList = ["apple", "banana", "kiwis", "mangos"];

Notice how we just made an object with 4 strings in it separated by commas. The variable shoppingList now holds all the fruits in one structure. Now that we have them all in one place, we also need to have a way to select them from the array. The great thing about arrays is that each element in the array has its own ID, so selecting is easy. Selecting can be done by doing something like this: shoppingList[0]. This will get the 0th element (array indices start at 0), which in this case is "apple". Doing shoppingList[1] will get "banana" and doing shoppingList[3] will get "mangos".

Array Methods: It is important to know some methods that arrays utilize to aid your programming. Among those include the following: sort() - sorts the array in its natural order (by number increasingly, by alphabetical order). Example: var x = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]; x.sort(); x is now [1, 1, 2, 3, 3, 5, 5, 6, 9] concat(array, ...) - Combines all the arrays in the parameters into the original array Example: var x = [1,2,3,4]; var y = [5, 6, 7]; var z = [8, 9, 10]; x.concat(y, z); x is now [1,2,3,4,5,6,7,8,9,10] reverse() - Reverse the ordering of the array. var x = [1,2,3]; x.reverse(); x is now [3,2,1];

Selecting Certain Parts of Arrays: To select certain parts of array, but not just one element is possible in JavaScript as well. The method that is already pre-written is called slice. The syntax for it is slice(start, end) just like in substring for strings. It starts from position start and ends before the end index. var x = [1,2,3,4,5]; and x.slice(2,4) would return [3,4].

Adding Elements Into Arrays It is possible to add to arrays even after arrays are defined. This is done by using the push or unshift functions of arrays.

Sometimes you want to add to the end of an array. Then you would use the push function. For example you have an array: var x = [1,2,3,4]; and you want to insert 5 into the end of the array. In order to accomplish this, you would type x.push(5); to add 5 to the end of the array. Most of the time inserting at the end of the array will suffice.

Still, occasionally it may be needed to insert an element at the front of the array. This is when you would use unshift, which inserts an element as you wanted it to. Doing x.unshift(0); on the previous array will change the array to [0, 1, 2, 3, 4, 5]; assuming 5 was pushed before.

Deleting Elements To remove the first or last element, the methods to use are shift and pop respectively. An example of how to use them is by taking the previous example: var x = [1,2,3,4,5]; and doing x.pop(); which will remove the 5. After that if x.shift() is called, then 1 would be removed leaving the array with only [2,3,4].

Create an array that stores all the numbers from 1 to 100 in increasing order.

var arr = [];
for (var i=1; i<=100; i++) {
     arr.push(i);
}

Write a function everyOther that takes an array and adds up every other element (starting from the first one) and returns the sum.

function everyOther(arr) {
     var sum = 0;
     for (var i=0; i < arr.length; i += 2) {
         sum += arr[i];
     }
     return sum;
}

Write a function named firstAndLast that takes in an array and checks if the first element and the last element in the array are equal.

function firstAndLast(arr) {
     return (arr[0] == arr[arr.length - 1]);
}

Notice that we did not need to use a loop here because we knew exactly which two positions in the array we needed to access in order to do the comparison.

Write a function called reverse that reverses the order of the elements in a given array. You can do this by creating another function that swaps the order of two elements. For each function, make sure to return the final result.

function reverse(arr) {
    for(i=0; i
        swap(arr,i,arr.length- 1 - i);
    }
    return arr;
}

function swap(arr, pos1, pos2) {
    temp = arr[pos2];
    arr[pos2]=arr[pos1];
    arr[pos1]=temp;
}

As we did in this exercise, it can be useful to create a "helper" method (like swap here) to make your code easier to read.

Write a function called range that takes a positive number and returns an array that contains all the numbers from 0 up to and including the number.

function range(n) {
     var nums = [];
     for (var i = 0; i <= n; i++) {
         nums.push(i);
     }
     return nums;
}

Create an array with the numbers one through five, spelled out in words. Remember to put quotes around them as they're strings.

var arr = ["one", "two", "three", "four", "five"];

Write a function called iff that takes an array and an item, and only adds the item to the end of the array if the item is a string AND the array contains the number 6. Make sure to return the resulting array (even if unchanged).

function iff(arr, item) {
     var isThere;
     if (typeof item=="string") {
         isThere = "no";
         for(i=0; i<=arr.length; i++) {
             if (arr[i] == 6) {
                 isThere = "yes";
             }
         }
     }
     if (isThere == "yes") {
     arr.push(item);
     }
     return arr;
}