使用Javascript数组将键和值与某个变量匹配的正确方法是什么？

Question

I'm trying to create a function in javascript in order to get a value that match an external variable.

I created an array of key/value. Then I made a function that will check if a value match to a variable. Then i will return the key of this value.

function findNumberFromMonth($data)
{    
var obj = {
    01: "Jan",
    02: "Feb",
    03: "Mar",
    04: "Apr",
    05: "May",
    06: "Jun",
    07: "Jul",
    08: "Aug",
    09: "Sep",
    10: "Oct",
    11: "Nov",
    12: "Dec"
    }

 for(var element in obj)
         {
             if($data == element.value )
                 {
                     $number = element.key
                 }
          return $number;
         }

}

I expected the output of "01" if i initialize $data as "Jan".

But i only got an undefined object. How may i process ?

Thank you for your replies.

Answer 1

If what you want to do is map month names to month numbers, your object is backwards:

function findNumberFromMonth($data)
{    
   var months = {
    "Jan": "01",
    "Feb": "02",
    "Mar": "03",
    // ...
    };

    return months[$data];
}

Answer 2

you can do this.

 var obj = { 01: "Jan", 02: "Feb", 03: "Mar", 04: "Apr", 05: "May", 06: "Jun", 07: "Jul", 08: "Aug", 09: "Sep", 10: "Oct", 11: "Nov", 12: "Dec" } var key = Object.keys(obj)[Object.values(obj).indexOf("Jun")] console.log(key) 

Answer 3

This can be done with find and Object.entries :

 function findNumberFromMonth(data) { const months = { 01: "Jan", 02: "Feb", 03: "Mar", 04: "Apr", 05: "May", 06: "Jun", 07: "Jul", 08: "Aug", 09: "Sep", 10: "Oct", 11: "Nov", 12: "Dec" }; return Object.entries(months).find(([key, val]) => data === val)[0]; } console.log(findNumberFromMonth('Oct')); 

Answer 4

When you use for(let x in obj) x is the key of the object.

 function findNumberFromMonth($data) { var obj = { 01: "Jan", 02: "Feb", 03: "Mar", 04: "Apr", 05: "May", 06: "Jun", 07: "Jul", 08: "Aug", 09: "Sep", 10: "Oct", 11: "Nov", 12: "Dec" } for(var key in obj) { if($data == obj[key]) return key; } } console.log(findNumberFromMonth('Jan')); 

Answer 5

if you need both keys and values simultaneously, use object.entries and iterate over it.

  const data = "Feb"; const obj = { "01": "Jan", "02": "Feb", "03": "Mar", "04": "Apr", "05": "May", "06": "Jun", "07": "Jul", "08": "Aug", } for (let [key, value] of Object.entries(obj)) { if(data === value ) { console.log(key); } } 

Answer 6

You assign $number variable in if statement. But return it in out of if statement. You must move return line to if statement and if not returned anything, you can return false value.

function findNumberFromMonth($data) {
  var obj = {
    01: "Jan",
    02: "Feb",
    03: "Mar",
    04: "Apr",
    05: "May",
    06: "Jun",
    07: "Jul",
    08: "Aug",
    09: "Sep",
    10: "Oct",
    11: "Nov",
    12: "Dec"
  }

  for (var key in obj) {
    if ($data === obj[key])
      return key;
  }

  return false;

}

console.log(findNumberFromMonth('Mar'));