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JavaScript facts for kids

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JavaScript is a scripting language for computers. It is often run in web browser applications to create dynamic content like a popup message or a live clock. It is not related to the programming language Java.


This script writes "Example" on the screen. The lines that start with // are comments; they show what the code does.

 1 <script type="text/javascript">
 2 function example()
 3 {
 4     var ex = document.createTextNode('Example'); //make the computer remember "Example", 
 5                                                  //so whenever you say "ex" the computer will append it with "Example"
 6     document.body.appendChild(ex);               //put the text on the bottom of the webpage
 7 }
 8 example(); 
10 /*
11  * The code below does almost the same thing as the code above, 
12  * but it shows "Example" in a popup box and is shorter.
13  *
14  * This is a comment too, by the way.
15  */
17 alert("Example");
18 </script>

The JavaScript is enclosed by <script></script> tags, to tell that it is a script and not text to be put onto the web page the JavaScript is running on. This script inserts the numbers 1 through 10 at the bottom of a webpage:

 1 <script type="text/javascript">
 2 for(var numOfTimesAround = 1; numOfTimesAround <= 10; numOfTimesAround++){
 4 document.body.innerHTML = document.body.innerHTML + numOfTimesAround + "<br>";
 5 /*
 6 * This puts the number, then a new line, at the end of the web page.
 7 * In javascript, using the + sign combines two words together.
 8 * So writing "Hello" + " World" would make "Hello World".
 9 * Or, writing 1 + "<br>" makes "1<br>", which is what we want.
10 */
12 }
14 </script>

The for() loop makes whatever code is between the { and the } happen more than one time. In this case, it keeps looping until numOfTimesAround is equal to 10, then it stops.

Differences between Java and Javascript

  • In Java, to make a variable (to make a computer remember something), you have to say what type of variable it is: a number, a word, a letter, or more. In JavaScript, this is not necessary.
  • In JavaScript, functions are stored as variables (unlike Java). This makes the following code okay in JavaScript:
function sayHi(){
sayHi = function(){
//alerts "Bye!" instead of "hi!" without giving an error
  • JavaScript runs in a web browser, but Java runs directly on a computer.
  • JavaScript is interpreted, but Java, in most cases, must be compiled. This means that JavaScript needs to be run by another computer program (an interpreter), but finished Java can be run as its own program.

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