JS data types

Basic data types: Number, String, Boolean, Null, Undefined, Symbol (ES6)
Reference data type: Object (In JS, all objects except basic data types are objects, and data is an object.Functions are objects, regular expressions are objects, etc.)

About Symbol: https://blog.csdn.net/weixin_34354945/article/details/91460921

The basic data type definition in JS is similar to the value type in C# (String is a reference type in C#), and so is the reference data type.
Continue reading, their storage methods are similar, the basic data type is stored on the stack, the reference data type is the specific value stored in the heap, and the reference address pointing to the specific value in the heap is stored on the stack.

The first sentence defines the object a, the secondThe sentence var c = a actually just copies the reference address of a and gives it to c. For the third sentence, after modifying the name of c to another value, the name of a has also changed, because the name attribute of c has been modified.When it is modified in the heap according to the reference address.When a accesses the object according to the same reference address, the object is naturally changed.

Here is another knowledge point: shallow copy and deep copy

Shallow copy:
Shallow copy will copy each attribute of the object in turn, but when the attribute value of the object is a reference type, it will be invalid, that is to say, onlyCopy one layer.

Object.assign is used here for shallow copy, similar toThe shallow copy method also has spread operator... , Array.prototype.slice(), Array.prototype.concat()

About the spread operator: http://www.fly63.com/article/detial/2516

Deep copy:
Deep copy copies variable values. For reference data, it recurses to basic types before copying.
The object after deep copy is completely isolated from the original object and does not affect each other. Modifications to one object will not affect the other object

 let obj = {name: 'Michael',age: 18,others: {hobbies: ['basketball', 'gambling'],team: 'Bulls',},};let obj1 = deepClone(obj);obj1.age = 19;obj1.others.team = 'test';console.log('obj', obj);console.log('obj1', obj1);// recursively implement deep copyfunction deepClone(obj) {if (obj instanceof RegExp) return new RegExp(obj);if (obj instanceof Date) return new Date(obj);if (obj === null || typeof obj !== 'object') return obj //If it is not a reference type, return directlylet newObj = new obj.constructor(); //if obj is an array, newObj=[]; if obj is an object, newObj={}for (let key in obj) {if (obj.hasOwnProperty(key)) { //Is it its own objectnewObj[key] = deepClone(obj[key]) //assignment}}return newObj}