How to use typeof in js

The typeof operator in JavaScript is used to determine the type of a value. It returns a string: "undefined": undefined variable "boolean": Boolean value "number": number "string": character String "object": object (including array) "function": function "symbol": Symbol value

typeof operator in JavaScript

The typeof operator is used to determine the data type of a JavaScript value. The syntax is as follows:

<code class="javascript">typeof value;</code>

Among them, value is the variable or expression to determine the data type.

Return value

The typeof operator returns a string indicating the type of the value. Possible return values ​​include:

• "undefined": undefined variable
• "boolean": Boolean value
• "number": number
• "string": string
• "object": object (including array)
• "function": function
• "symbol": Symbol value

Example

<code class="javascript">const x = 10;
console.log(typeof x); // 输出: "number"

const y = "hello";
console.log(typeof y); // 输出: "string"

const z = [1, 2, 3];
console.log(typeof z); // 输出: "object"

const f = function() {};
console.log(typeof f); // 输出: "function"

const s = Symbol("foo");
console.log(typeof s); // 输出: "symbol"</code>

It is worth noting that the return value of typeof operator for null is "object". This is because in JavaScript, null is treated as an object, not a primitive type.

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