Typeof usage in JavaScript

In JavaScript, typeof is an operator used to determine the data type of a given variable. Can be used to determine whether a variable is a string, number, Boolean, function, object, or undefined data type.

#In JavaScript, typeof is an operator used to determine the data type of a given variable. It can be used to determine whether a variable is a string, number, boolean, function, object, or undefined data type. Here are several examples of typeof usage:

console.log(typeof "Hello"); // 输出: string
console.log(typeof 10); // 输出: number
console.log(typeof true); // 输出: boolean
function greetings() {
return "Hello";
}
console.log(typeof greetings); // 输出: function
let person = {name: "John", age: 30};
console.log(typeof person); // 输出: object
let x;
console.log(typeof x); // 输出: undefined

It should be noted that typeof null returns "object", which is a known bug in JavaScript. So use caution when detecting data types.

However, typeof is sometimes not very accurate. For example, for arrays and null, the behavior of typeof may not be what we want:

let arr = [1, 2, 3];
console.log(typeof arr); // 输出: object
let y = null;
console.log(typeof y); // 输出: object

In general, typeof is a common operator used to determine the data type of a variable, but it also has some Restrictions need to be noted when using.

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