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Conditions

if-statement

The if-statement is easiest condition statement that follows this syntax:

if (condition) { do something... }

[IMPORTANT NOTE] As long the condition interprets to true any non-null value the is executed.

{% runkit %} // conditions are met if (true) { console.log("foo") } if ("something") { console.log("bar") }

// conditions are not met if (false) { console.log("abc") } if (null) { console.log("xyz") } {% endrunkit %}

And of course If-statements can be nested.

{% exercise %} What should be the values of the variables 'a' & 'b' so that the 'c' will be equal to "Yes"?

{% initial %} var a = var b = var c = null;

if (a === "foo") { if (b === "bar") { c = "Yes"; } if (b === "xyz") { c = "No"; } }

{% solution %} var a = "foo"; var b = "bar"; var c = null;

if (a === "foo") { if (b === "bar") { c = "Yes"; } if (b === "xyz") { c = "No"; } }

{% validation %} assert(c === "Yes"); {% endexercise %}

else-statement

You may use the else and else if statement if you want to create multiple conditions.

if (condition1) {
    // statement 1
} else if (condition 2) {
    // statement 2
} else if (condition N) {
    // statement N
} else (condition default) {
    // executes if all conditions was not met
}

For example:

{% runkit %} let a = "foo";

if (a === "abc") { console.log("abc"); } else if (a === "xyz") { console.log("xyz"); } else { console.log("foo"); } {% endrunkit %}

Comparators and Chaining Conditions

Javascript supports the following comparators:

Operator What it does
== equal to
=== equal to & equal type
!= not equal to
!=== not equal to or not equal type
> greater than
< less than
>= greater than or equal to
<= less than or equal to

You may also chain conditions and (&&) and or (||). Some examples:

{% runkit %} let age = "18";

if (age < 18) { console.log("minor"); } else if (age >= 18 && age < 60) { console.log("legal"); } else { console.log("senior"); } {% endrunkit %}

{% exercise %} Add the second condition below so that the status will be "legal" if the age is greater than or equal to 18 and less than 65?

{% initial %} let age = 34; let status = null;

if (age < 18) { status = "minor"; } else if (place your Answer here...) { status = "legal"; } else { status = "senior"; }

{% solution %} let age = 34; let status = null;

if (age < 18) { status = "minor"; } else if (age >= 18 && age < 65) { status = "legal"; } else { status = "senior"; }

{% validation %} assert(status === "legal"); {% endexercise %}