Example of using JS to determine whether an element is an array

Here are the types of data that can be verified

let a = [1,2,3,4,5,6];
 let b = [
 {name: 'Zhang Fei', type: 'tank'},
 {name: 'Guan Yu', type: 'soldier'},
 {name: 'Liu Bei', type: 'shooter'},
 ];
 let c = 123;
 let d = 'www';
 let e = {name: 'Angela', type: 'mage'};

1. Through Array.isArray()

Array.isArray() can determine whether an element is an array, if so, it returns true, otherwise it returns false

console.log(Array.isArray(a)); // true
 console.log(Array.isArray(b)); // true
 console.log(Array.isArray(c)); // false
 console.log(Array.isArray(d)); // false
 console.log(Array.isArray(e)); // false

2. Judge by instanceof

The instanceof operator is used to detect whether an instance belongs to an object's prototype chain.

console.log(a instanceof Array); // true
 console.log(b instanceof Array); // true
 console.log(c instanceof Array); // false
 console.log(d instanceof Array); // false
 console.log(e instanceof Array); // false

It can also be used to judge objects

console.log(e instanceof Object); // true

To determine whether it is an array, we need to check whether the Arrray.prototype property exists in the prototype chain of the variable array (a, b). Obviously, a and b are arrays and have the Arrray.prototype property, so it is true.

3. Judge by the constructor of the object constructor

Each instance of Object has a constructor that stores the function that creates each object.

console.log(a.constructor === Array); // true
console.log(b.constructor === Array); // true

The following includes other data type validations

console.log(c.constructor === Number); // true
console.log(d.constructor === String); // true
console.log(e.constructor === Object); // true

4. Judge by Object.prototype.toString.call()

Look up the call through the prototype chain

console.log(Object.prototype.toString.call(a) === '[object Array]'); // true
console.log(Object.prototype.toString.call(b) === '[object Array]'); // true

The following includes other data type validations

console.log(Object.prototype.toString.call(c) === '[object Number]'); // true
console.log(Object.prototype.toString.call(d) === '[object String]'); // true
console.log(Object.prototype.toString.call(e) === '[object Object]'); // true

5. Judge by isPrototypeOf() on the object prototype chain

The Array.prototype property is the prototype of the Array constructor, which contains a method isPrototypeOf() that is used to test whether an object exists in the prototype chain of another object.

console.log(Array.prototype.isPrototypeOf(a)); // true
 console.log(Array.prototype.isPrototypeOf(b)); // true
 console.log(Array.prototype.isPrototypeOf(c)); // false
 console.log(Array.prototype.isPrototypeOf(d)); // false
 console.log(Array.prototype.isPrototypeOf(e)); // false

Summarize

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