In HTML, JavaScript statements are "instructions" to be "executed" by the web browser.
This statement tells the browser to write "Hello Dolly." inside an HTML element with id="demo":
Most JavaScript programs contain many JavaScript statements.
The statements are executed, one by one, in the same order as they are written.
In this example, x, y, and z is given values, and finally z is displayed:
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JavaScript programs (and JavaScript statements) are often called JavaScript code. |
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Semicolons separate JavaScript statements.
Add a semicolon at the end of each executable statement:
When separated by semicolons, multiple statements on one line are allowed:
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On the web, you might see examples without semicolons. Ending statements with semicolon is not required, but highly recommended. |
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JavaScript ignores multiple spaces. You can add white space to your script to make it more readable.
The following lines are equivalent:
For best readability, programmers often like to avoid code lines longer than 80 characters.
If a JavaScript statement does not fit on one line, the best place to break it, is after an operator:
JavaScript statements can be grouped together in code blocks, inside curly brackets {...}.
The purpose of code blocks this is to define statements to be executed together.
One place you will find statements grouped together in blocks, are in JavaScript functions:
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In this tutorial we use 4 spaces of indentation for code blocks. You will learn more about functions later in this tutorial. |
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JavaScript statements often start with a keyword to identify the JavaScript action to be performed.
Here is a list of some of the keywords you will learn about in this tutorial:
| Keyword | Description |
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| break | Terminates a switch or a loop |
| continue | Jumps out of a loop and starts at the top |
| debugger | Stops the execution of JavaScript, and calls (if available) the debugging function |
| do ... while | Executes a block of statements, and repeats the block, while a condition is true |
| for | Marks a block of statements to be executed, as long as a condition is true |
| function | Declares a function |
| if ... else | Marks a block of statements to be executed, depending on a condition |
| return | Exits a function |
| switch | Marks a block of statements to be executed, depending on different cases |
| try ... catch | Implements error handling to a block of statements |
| var | Declares a variable |
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JavaScript keywords are reserved words. Reserved words cannot be used as names for variables. |
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