Array.join("") 方法不起作用 JavaScript

Question

I'm confused about why array.join("") is not working properly in this function.

If the letter is am it will show 0 and the otherwise is 1 convertBinary("house") ➞ "01110"

function convertBinary(str) {
  var jack=str.split("")
  return jack.map(function(e) {
    var array=[]
    if(e.match(/[abcdefghijklm]/g)) {
      array.push(0)
    } else {
      array.push(1)
    }
    return array.join("");
  })
}

Where did I go wrong.

Answer 1

You need to apply the .join("") to the result of the map() call, instead of inside the map() inner function, which also should return just 0 or 1 for each character.

Also it would be better to use regex.test(str) because we are only interested in if there is a match (true or false), see eg what is the difference between .match and .test in javascript .

Like this:

 function convertBinary(str) { var jack = str.split("") return jack.map(function(e) { if (/[abcdefghijklm]/.test(e)) { return 0; } else { return 1; } }).join(""); } console.log(convertBinary("house"));

Answer 2

The array.join() must be outside the jack.map() function, like this:

var jack_bin = jack.map(function(e)
{
    var array=[]
    if(e.match(/[abcdefghijklm]/g))
    {
        return '0';
    }
    else
    {
        return '1';
    }
})
return jack_bin.join("");

Answer 3

Please try this solution

 function convertBinary(str) { const jack = str.split(''); const binArr = jack.map(e => { if (e.match(/[abcdefghijklm]/g)) { return 0; } else { return 1; } }); return binArr.join(''); } console.log(convertBinary('house'))

Answer 4

You could short it a bit by using a chain of methods and use test instead of match , because you need a boolean value, not an array of matched items/null.

Then you need to take eiter 1 or 0 and join the result for getting a string.

 function convertBinary(string) { return string .split("") .map(function(e) { return /[abcdefghijklm]/.test(e) ? 1: 0; }) .join(''); } console.log(convertBinary("house")) // "01110"

Answer 5

Initialize array and return array.join() outside the map function:

 function convertBinary(str) { var jack=str.split(""); var array = jack.map(function(e){ if(e.match(/[abcdefghijklm]/g)){ return 0; } else { return 1; } }) return array.join(""); } console.log(convertBinary('house'));

Answer 6

The key point here is that it should be fixed as jack.map(...).join() , because jack.map() returns an array.

 function convertBinary(str) { var jack=str.split("") return jack.map(function(e) { var array=[] if(e.match(/[abcdefghijklm]/g)) { array.push(0) } else { array.push(1) } return array; }).join("") } console.log(convertBinary("house")); // output is '01110'