The if statement executes a statement if a specified condition is true. If the condition is false, another statement can be executed.
if (condition) statement1 [else statement2]
condition
statement1
condition
evaluates to true. 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
condition
evaluates to false and the else
clause exists. Can be any statement, including block statements and further nested if
statements.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 like 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 the true and false values of the Boolean object. Any value that is not undefined
, null
, 0
, NaN
, or the empty string (""
), and any object, including a Boolean object whose value is false, evaluates to true when passed to a conditional statement. For example:
var b = new Boolean(false); if (b) // this condition evaluates to true
if...else
if (cipher_char === from_char) { result = result + to_char; x++; } else { result = result + clear_char; }
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 > 5) { } else if (x > 50) { } else { }
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 the right thing */ }
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 the right thing */ }
Created by Mozilla Contributors, license: CC-BY-SA 2.5