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On the concept of object attribute and stack in JavaScript
2021-08-27 02:06:29 【Antarctic ice】
This is my participation 8 The fourth of the yuegengwen challenge 23 God , Check out the activity details :8 Yuegengwen challenge
Preface
Hello everyone , Today we are going to talk JavaScript The concept of object properties and stack in , For a small partner who has no academic background , The concept is still easy to be confused , So let's talk about this problem today .
The goal of the article is
Let's take a look at the goal of this article , Please detour , Because this article basically extracts my notes when I first started ~
a key
1. Can get and set the value of object properties
2. Ability to traverse objects
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understand
1. Know that the memory is divided into two areas: stack and heap
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Action object
The operation object is relatively simple , Be familiar with basic operation objects and methods .
Get the value of the object property
Be careful : If there are no properties in the object , The return is undefined.
var obj = {
name: ' Xiao Ming ',
age: 20
}
alert(obj.name) // ' Xiao Ming '
alert(obj.sex) // undefined
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Add properties and assign values to the object
var obj = {
name: 'ls'
age: 20
}
// Add properties and assign values to the object
obj.sex = ' male '
console.log(obj) // {name: 'ls', age: 28, sex:' male '}
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Manipulate the properties of an object through bracket syntax
grammar : object [ ' Property name ' ]
var stu01 = {
name:' The small white ',
age:28,
sex:true,
getInfo:function(){
return ' My name is :'+this.name + ', Age :'+ this.age + ', Gender :' + this.sex
}
}
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The operation of obtaining is as follows :
alert(stu01.name) // The small white
alert(stu01['name']) // The small white
alert(stu01.getInfo()) // My name is Xiaobai , Age 28, Gender true
alert(stu01['getInfo']()) // My name is Xiaobai , Age 28, Gender true
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assignment , The following two ways of writing code work the same :
stu01.name = ' Little black '
stu01['name'] = ' Little black '
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Traverse all properties in the object
adopt for..in loop , Traversing the properties of an object
grammar : for( var Variable name in Traversed objects ){ Code executed in a loop }
var obj = {
name: 'zs',
age: 18,
sayHi:function(){
console.log('hi');
}
};
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There are several properties in the object ,for The loop will be executed several times
During the cycle , The attributes in the object are assigned to key Variable
Use bracket syntax in the loop
for(var key in obj) {
console.log(key + "==" + obj[key]);
}
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Delete an attribute in an object
var obj = {
name: 'zs',
age: 18
}
console.log(obj.age) // 18
delete obj.age
console.log(obj.age) // undefined
console.log(obj) // {name: 'zs'}
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Stack space and heap space in memory
js All of the code must be loaded into memory for execution , In fact, the memory is divided into regions , such as , There is a stack in memory and Stack two areas
js Medium 6 Type of data , It is divided into two categories : Basic data types and reference data types
The stack is equivalent to the address , The heap is equivalent to the actual storage place
- Basic data types are stored in stack space
- Reference data types are stored in heap space
The diagram is as follows :
Basic data type and reference data type are passed as parameters
Basic data type assignment
var num1 = 1;
var num2;
num2 = num1; // hold num1 Clone a copy of the value assigned to num2
console.log(num2); //1
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The diagram is as follows :
Reference data type assignment
var obj = {
name: 'zs'
}
var num2
num2 = obj
console.log(num2) // { name: 'zs'}
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The diagram is as follows :
Postscript
Hello, wow , I'm the Antarctic ice , A front-end engineer whose technology is proportional to his appearance , Advocate getting to the point to solve the front-end problems , I hope my blog has helped you .
Pay attention to me , Go along the front road . Hey ha ~
copyright notice
author[Antarctic ice],Please bring the original link to reprint, thank you.
https://en.qdmana.com/2021/08/20210827020626187w.html
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