What are the methods to determine data type in js

In JavaScript, there are three ways to determine the data type: the typeof operator returns a string representing the data type of the variable. The instanceof operator checks whether an object belongs to a specific constructor. The Object.prototype.toString.call method returns a string representing the variable type, which is more accurate than typeof.

How to determine the data type in JavaScript

In JavaScript, determining the data type is a common task. The following introduces several common methods:

typeof operator

typeof operator returns a string representing the data type of the variable. It is the simplest method, but it cannot differentiate between some similar data types.

Syntax:

<code>typeof variable;</code>

For example:

<code>console.log(typeof "Hello"); // "string"
console.log(typeof 123); // "number"
console.log(typeof true); // "boolean"
console.log(typeof null); // "object" (错误地识别为对象)</code>

instanceof operator

instanceofOperator checks for one Whether the object belongs to a specific constructor. It is useful for differentiating complex data types such as arrays, functions, and date objects.

Syntax:

<code>variable instanceof constructor;</code>

For example:

<code>console.log([] instanceof Array); // true
console.log(function() {} instanceof Function); // true
console.log(new Date() instanceof Date); // true</code>

Object.prototype.toString.call Method

Object.prototype The .toString.call method returns a string representing the variable type. It is more accurate than the typeof operator and can differentiate between arrays, functions and date objects.

Syntax:

<code>Object.prototype.toString.call(variable);</code>

For example:

<code>console.log(Object.prototype.toString.call([])); // "[object Array]"
console.log(Object.prototype.toString.call(function() {})); // "[object Function]"
console.log(Object.prototype.toString.call(new Date())); // "[object Date]"</code>

Notes

• typeofOperator would incorrectly identify null as an object. The
• instanceof operator cannot distinguish between native constructors and custom constructors.
• Object.prototype.toString.call method can provide more accurate data type information, but its syntax is relatively complex.

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