The if
statement executes a statement if a specified condition is truthy. If the condition is falsy, another statement can be executed.
Syntax
if (condition) statement1 [else statement2]
condition
- An expression that is considered to be either truthy or falsy.
statement1
- Statement that is executed if condition is truthy. Can be any statement, including further nested
if
statements. To execute multiple statements, use a block statement ({ ... }
) to group those statements. To execute no statements, use an empty statement. statement2
- Statement that is executed if
condition
is falsy and theelse
clause exists. Can be any statement, including block statements and further nestedif
statements.
Description
Multiple if...else
statements can be nested to create an else if
clause. Note that there is no elseif
(in one word) keyword in JavaScript.
if (condition1) statement1 else if (condition2) statement2 else if (condition3) statement3 ... else statementN
To see how this works, this is how it would look if the nesting were properly indented:
if (condition1) statement1 else if (condition2) statement2 else if (condition3) ...
To execute multiple statements within a clause, use a block statement ({ ... }
) to group those statements. In general, it is a good practice to always use block statements, especially in code involving nested if
statements:
if (condition) { statements1 } else { statements2 }
Do not confuse the primitive Boolean values true
and false
with truthiness or falsiness of the Boolean
object. Any value that is not false
, undefined
, null
, 0
, -0
, NaN
, or the empty string (""
), and any object, including a Boolean object whose value is false
, is considered truthy when used as the condition. For example:
var b = new Boolean(false); if (b) // this condition is truthy
Examples
Using if...else
if (cipher_char === from_char) { result = result + to_char; x++; } else { result = result + clear_char; }
Using else if
Note that there is no elseif
syntax in JavaScript. However, you can write it with a space between else
and if
:
if (x > 50) { /* do something */ } else if (x > 5) { /* do something */ } else { /* do something */ }
Assignment within the conditional expression
It is advisable to not use simple assignments in a conditional expression, because the assignment can be confused with equality when glancing over the code. For example, do not use the following code:
if (x = y) { /* do something */ }
If you need to use an assignment in a conditional expression, a common practice is to put additional parentheses around the assignment. For example:
if ((x = y)) { /* do something */ }
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'if statement' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
if...else | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support 3 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support 0.1.100 |
Legend
- Full support
- Full support