js type detection
1. The typeof operator returns a string indicating the type of the uncalculated operand
Syntax: typeof operand
Parameters: operand is an expression representing an object or primitive value whose type will be returned
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Types of
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result
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Undefined
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"undefined"
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Number
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"number"
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String
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"string"
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Boolean
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"boolean"
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Null
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"object"
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Object , Array
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"object"
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any other object
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"object"
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example:
typeof 37 === 'number';
typeof 3.14 === 'number';
typeof 'abv' === 'string';
typeof (typeof 12) === 'string'; //typeof 总是返回一个字符串
typeof 1/0 === 'NaN';
2. The instanceof operator is used to test whether an object has a constructor's prototype property in its prototype chain.
Syntax: object instanceof constructor
Parameters: object The object to detect
constructor a constructor
Description: The instanceof operator is used to check whether constructor.prototype exists on the prototype chain of the parameter object.
example:
//定义构造函数
function C(){}
function D(){}
var o = new C();
o instanceof C; //true
o instanceof D; //false
3.isArray detection array
function isArray(obj) {
return Object.prototype.toString.call(obj) === '[object Array]';
}
I hope my experience of entering the pit is helpful to you, may the Holy Light be with you