为什么返回未定义？

Question

I want to store as the following method, and get the constant value, by querying using key to find value or by value to find the key

function my_reference() {
  return {
    30:'',
    31:'ERR591',
    32:'ERR761',
    33:'ERR671',
    34:'ERR551',

  };
}

console.log( my_reference[31], 
             my_reference.31, 
             my_reference().31,
             my_reference()[31]
);

Answer 1

 my_reference[31], 

Trying to read a property (which doesn't exist) of a function. The property is on the object that is the return value of calling the function.

 my_reference.31, 

Trying to use a number as an identifier. This isn't allowed.

 my_reference().31, 

Trying to use a number as an identifier. This isn't allowed.

 my_reference()[31] 

This works

Answer 2

You have to call function if you want it to return result, function called by :

my_reference()

So the both first lines will not work because my_reference will return the function it self and not call it :

my_reference[31]
my_reference.31

The third also will not work console.log(my_reference().31); because attribute can't be numeric.

Hope this helps.

Answer 3

您需要使用my_reference()执行该函数， my_reference()访问您想要的属性。.但是javascript对象中的键始终是字符串：

console.log(my_reference()['31']);

Answer 4

You don't need to use a function to store the references:

var reference = {
    30:'',
    31:'ERR591',
    32:'ERR761',
    33:'ERR671',
    34:''
};

console.log(reference[31]);

Answer 5

Here is the fixed code

function my_reference() {
  return {
    _30:'',
    _31:'ERR591',
    _32:'ERR761',
    _33:'ERR671',
    _34:'ERR551'
  };
}

var f = my_reference();

console.log(f["_31"]); 
console.log(f._31);
console.log(my_reference()._31);
console.log(my_reference()["_31"]); 

Variables can't be named with just numbers The first two should be the returned object