if...else

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 the else clause exists. Can be any statement, including block statements and further nested if 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 */
}

Using an assignment as a condition

You should almost never have an if...else with an assignment like "x = y" as a condition:

if (x = y) {
  /* do something */
}

However, in the rare case you find yourself wanting to do something like that, the while documentation has a Using an assignment as a condition section with an example showing a general best-practice syntax you should know about and follow.

Specifications

Specification
ECMAScript Language Specification
# sec-if-statement

Browser compatibility

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See also