JavaScript Statements

A computer program is a list of instructions that a computer needs to execute.

In programming languages, these programming instructions are called statements.

A JavaScript program is a list of programming statements.

Statements are used in JavaScript to specify the flow of the program.

JavaScript statements are composed of the following items:Values, operators, expressions, keywords, and comments.

This statement tells the browser to write the content "Hello world" inside the HTML element with id="para":

document.getElementById("para").innerHTML = "Hello world";

Most JavaScript programs contain many JavaScript statements.

Statements are executed in the order they are written.

var a, b, sum;//　Statement　1
a =　20;　　　//　Statement　2
b =　30;　　　//　Statement　3
sum = a　+　b;　　//　Statement　4

Statements define the operations that the script will execute and how they will be executed.

Semicolon (;)

And C, C ++Like in Java, simple statements in JavaScript are usually followed by a semicolon character.

But if each statement is placed on a separate line, JavaScript allows you to omit this semicolon.

var x =　20
var y =　30

But when formatted in a single-line format as shown below, a semicolon must be used:

var x =　20; var y =　30;

JavaScript spaces

JavaScript ignores spaces, tabs, and newline characters that appear in the JavaScript program.

You can add spaces in the script to make it more readable.

The following two lines are equivalent:

var greet = "Hello world";
var greet = "Hello world";

It is generally recommended to place spaces around the operator ( +-* /）spaces around, to enhance readability:

var sum = a　+　b　;

JavaScript line length and newline characters

To ensure the best readability, it is advisable to avoid code lines that exceed80 characters.

If the JavaScript statement does not fit on one line, the best place to break the line is at the operator ( +-* /）after:

document.getElementById("para").innerHTML = "20+3The sum of 0 is "　+
sum;

JavaScript code block

JavaScript statements can be grouped together within a code block {...}.

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

InIn JavaScript functionsYou will find that statements grouped together in a block are placed at one place.

function myFunc() {
　　document.getElementById("p1").innerHTML = "Hey, there!";
　　document.getElementById("p2").innerHTML = "How are you doing?";
}

JavaScript keywords

JavaScript statements usually end withKeywordStarts with, to identify the JavaScript operation to be executed.

Below is a list of some keywords you will learn about in this tutorial: