JavaScript-what is the meaning of [] in the JS function?

function returnfunc (propertyName) {  return function (obj) {             //-----这行定义并返回了一个闭包，也被称之为一个匿名函数    return obj[propertyName];         //这里用方括号法访问属性，因为属性是变量（returnfunc（）函数的参数）  };}var savefunc = returnfunc("name");     //调用returnfunc（）var result = savefunc({name:"Picasso"});//调用savefunc（）alert(result);                        //返回字符串“Picasso”

Name: "Picasso" in Savefunc ({name: "Picasso"})

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function returnfunc (propertyName) {  return function (obj) {             //-----这行定义并返回了一个闭包，也被称之为一个匿名函数    return obj[propertyName];         //这里用方括号法访问属性，因为属性是变量（returnfunc（）函数的参数）  };}var savefunc = returnfunc("name");     //调用returnfunc（）var result = savefunc({name:"Picasso"});//调用savefunc（）alert(result);                        //返回字符串“Picasso”

Name: "Picasso" in Savefunc ({name: "Picasso"})

A dot, followed by a [] is a representation of an object's property, except that it contains a string, which is a string.
A variable is generated after the first executionvar propertyName = "name";
And then:

var savrfunc = function(obj){    return obj[propertyName];}

It then executes the above function and returns the return value to result;
The effect on the inside is equivalent to the following:

var obj = {name:"Picasso"};return obj[propertyName]//上面 已经有这个变了 值是name ；所以就是返回了 obj.name ,相当于把 Picasso给返回出去了。

As with the. function, the usage is different

var text ='prop';var obj = {  prop:123};obj.prop//123obj.text//undefinedobj[text]//123

PropertyName is the attribute name, Person[propertyname] is person[' name ']

return obj[propertyName]; //这里用方括号法访问属性，因为属性是变量（returnfunc（）函数的请输入代码参数）

It's all in your notes.
The properties of an object are accessed in two ways:

1. The form of obj.attr, simple writing

2. OBJ[ATTR], the property name can be the form of a variable

. and [] Both can access the object

Source: JavaScript Standard reference Tutorial (Alpha), by Ruan Yi Feng

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