How to determine whether variables are equal in javascript

Judgment method: 1. Use the equality operator "==" or "==="; 2. Use the toString() method in the array; 3. Use the "Object.is()" method; 4 , first use "JSON.stringify()" to convert the object or array into a string type, and then use "===" for equality comparison.

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

Ways to determine whether variables are equal

To determine whether variables are equal, there are roughly the following ways

• ==and===;
• Use thetoStringmethod in the array;
• in ES6TheObject.ismethod;
• usesJSON.stringifyto convert toStringtype for comparison;

==and===

##==are conversion type comparison operations operator,===is a strict comparison operator. When the data types are the same, using==will generally not cause problems.

let num = 5; let num2 = 5; num == num2;//true num === num2;//true

But when the data types are inconsistent,

==will do some implicit type conversion.

let num = 5; let str = '5'; num == str;//true num === str;//false '' == false;//true '' === false;//false null == undefined;//true null === undefined;//false

Implicit conversion type can bring some convenience, but it may also cause

bugsthat are not easy to find, so it is more recommended to use===for comparison , which is one of the reasons whyTSis popular.

In addition, the above lists are all comparisons of basic data types, and there will be certain limitations when using

===to compare reference types.

let a = {xx: 1}; let b = a; a === b;//true let c = {xx: 1}; let d = {xx: 1}; c === d;//false

When comparing reference types,

===compares whether the reference of the variable is the same,rather than the value. When the reference is different, # will be returned ##false.It can be seen that

===

is not a silver bullet that is invincible. When comparing whether objects are equal, other more reliable methods are needed.[Recommended learning:

javascript advanced tutorial

]

Array toString methodThe front end is given to the back end When passing parameters from the end, the backend sometimes requires multiple parameters separated by

and

. TheArray toStringmethod is more useful. This method can also be used for array comparison.

let arr = [1,3,5,7,9]; let arr2 = [1,3,5,7,9]; arr.toString() === arr2.toString();//true "1,3,5,7,9"

However, there are certain limitations. It cannot be used to compare arrays of two dimensions and above, and it cannot contain

null

,undefined, andobject##. #,function, etc., otherwise it is easy to make errors, as follows

[1,3,5,[2,4,6]].toString();//"1,3,5,2,4,6" [1,null,undefined,'',2].toString();//"1,,,,2" [{xx:2},window,1,2].toString();//"[object Object],[object Window],1,2"

Object.is method

Object. is

is a new method in ES6. It is very similar to

===and is also used to compare whether two values are equal.

Object.is(1,1);//true Object.is('str','str');//true Object.is({},{});//false

The difference is in judging0

and

-0,NaNandNaN.

+0 === -0 //true NaN === NaN //false Object.is(+0, -0) //false Object.is(NaN, NaN) //true

When dealing with compatibility issues, polyfill can be written like this.

if (!Object.is) { Object.is = function(x, y) { if (x === y) { // 针对+0 不等于 -0的情况 return x !== 0 || 1 / x === 1 / y; } else { // 针对NaN的情况 return x !== x && y !== y; } }; }

JSON.stringify

JSON.stringify

method is used to convert an object or array into a JSON string , the resulting string can be used for object comparison.

let obj = {name: 'lin', age: 24}; let obj2 = {name: 'lin', age: 24}; obj === obj2;//false JSON.stringify(obj) === JSON.stringify(obj2);//true

JSON.stringify

makes up for the limitation that

===cannot accurately compare objects, but it also has certain limitations. When encounteringundefined,functionandsymbolvalues are ignored.In addition, it is worth mentioning that usingJSON.parse

and

JSON.stringifycan realize object deep copy, with the same limitations as above.

When to use them

Different scenarios may have different requirements. If only basic data types are compared, then===

is enough. If you want to "

Once and for all", then it is undoubtedly necessary to pay a certain cost to use a custom method.In the daily repeated development, you still need to explore more.

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