JavaScript statements

Author: MDBootstrap

JavaScript statements examples:

            var x, y, z;  // Statement 1
            x = 5;    // Statement 2
            y = 6;    // Statement 3
            z = x + y;  // Statement 4

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JavaScript Programs

A computer program is a list of "instructions" to be "executed" by a computer.

In a programming language, these programming instructions are called statements.

A JavaScript program is a list of programming statements. In most of cases JavaScript programs are executed by the web browser.

JavaScript Statements

JavaScript statements are composed of:

Values, Operators, Expressions, Keywords, and Comments.

This statement tells the browser to write "Hello Dolly." inside an HTML element with id="demo":

                      document.getElementById("demo").innerHTML = "Hello Dolly.";

Most JavaScript programs contain many JavaScript statements.

The statements are executed, one by one, in the same order as they are written.

Note: JavaScript programs (and JavaScript statements) are often called simply JavaScript code.

Semicolons ;

Semicolons separate JavaScript statements.

Add a semicolon at the end of each executable statement:

                    var a, b, c;
                    a = 5;
                    b = 6;
                    c = a + b;
                    document.getElementById("demo").innerHTML = c;

When separated by semicolons, multiple statements on one line are allowed:

                    a = 5; b = 6; c = a + b;

Note: On the web, you might see examples without semicolons. Ending statements with semicolon is not required, but highly recommended.

JavaScript White Space

JavaScript ignores multiple spaces. You can add white space to your script to make it more readable.

The following lines are equivalent:

                    var person = "Hege";
                    var person="Hege";

A good practice is to put spaces around operators ( = + - * / ):

                    var x = y + z;

JavaScript Line Length and Line Breaks

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:

                      document.getElementById("demo").innerHTML =
                      "Hello Dolly!";

JavaScript Code Blocks

JavaScript statements can be grouped together in code blocks, inside curly brackets {...}.

The purpose of code blocks is to define statements to be executed together.

One place you will find statements grouped together in blocks, is in JavaScript functions:

                      function myFunction() {
                        document.getElementById("demo1").innerHTML = "Hello Dolly!";
                        document.getElementById("demo2").innerHTML = "How are you?";

Note: You will learn more about functions later in this tutorial.

JavaScript Keywords

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:

Do not worry if the terms below are unclear to you. You will learn everything in future lessons. The following table only serves to communicate that such concepts exist.

Keyword Description
break Terminates a switch or a loop
continue Breaks current iteration and jumps to the next one
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 and returns a value.
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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