将数组转成字符串，用分隔符分隔字符串 - JavaScript

Question

Define a function, myJoin , that accepts up to two arguments:

1. array
2. separator (string, optional)

myJoin should return a string with all of the elements from the array joined together. The separator should separate the joined elements:

myJoin(['a', 'b', 'c'], '+'); // => "a+b+c"

If separator is undefined, use ',' as the default separator.

myJoin(['Peter', 'Paul', 'Mary']); // => "Peter,Paul,Mary"

If any elements in the array are undefined or null , they should be replaced with an empty string in the returned string.

myJoin(['hello', undefined, 'world'], '-'); // => "hello--world"

I can't use the built-in join method.

Link to codepen for testing

So far I have tried:

function myJoin (array, separator) {

  let newString = "";

  if (separator = undefined) {
    separator === ",";
  }

  else {

    for (let i = 0; i < array.length; i++) {
      newString = i + separator;
    }

  }

  newString = array.toString();

  return newString;

}

console.log(myJoin(['a', 'b', 'c'], '+'));

^ This is not combining the elements of the string together with the separator, and is actually returning a,b,c twice. Any idea why?

EDIT : First update to code after @Jonas Wilms' suggestions:

function myJoin (array, separator) {

  let newString = "";

  if (separator === undefined) {
    separator === ",";
  }

  for (let i = 0; i < array.length; i++) {
    newString += array[i] + separator;
  }

  return newString;

}

This seems to be working in my VS Code console but not in the CodePen.

Answer 1

try

array.reduce( (s,x,i) => s+(i>0 ? separator : '') + (x==null ? '' : x), '') 

 function myJoin(array, separator=',') { return array.reduce( (s,x,i) => s+(i>0 ? separator : '') + (x==null ? '' : x), '') } console.log( myJoin(['a', 'b', 'c'], '+') ); console.log( myJoin(['Peter', 'Paul', 'Mary']) ); console.log( myJoin(['hello', undefined, 'world'], '-') );

We use here standard js functionalities: arrow functions , array reduce and ternary operator . If i>0 (not true only for first element) we add separator to output string s . If x is undefined or null we add to s empty string - or x value in other case.

Answer 2

A few hints:

• Don't mix up the assignment ( = ) and comparison ( === ) operators. if(a = b) is a mistake in 99% of the cases.

• array.toString() does call array.join() internally, I'd consider that as cheating, also I'm not sure what you want to achieve with that (I mean newString should already contain the wanted result if you do the loop correctly, shouldn't it?)

• i is the index in your array to get the value at that position use array[i] .

• I don't think that your loop should be in the else { branch, I don't think you need that else at all (as you always want to join the array by looping over it).

• with newString = you reassign newString and loose the previous value, you might want to use newString += to append a value to it.

Answer 3

Use map and forEach with a template string like so:

 function myJoin(arr, sep = ",") { arr = arr.map(e => [undefined, null].includes(e) ? "" : e); var result = ""; arr.forEach((e, i) => result += `${i ? sep : ""}${e}`); return result; } console.log(myJoin(['Peter', undefined, 'Paul', null, 'Mary', 'Jack'], "-"));

ES5 syntax:

 function myJoin(arr, sep) { sep = sep || ","; arr = arr.map(function(e) { return [undefined, null].includes(e) ? "" : e; }); var result = ""; arr.forEach(function(e, i) { result += (i ? sep : "") + e; }); return result; } console.log(myJoin(['Peter', undefined, 'Paul', null, 'Mary', 'Jack'], "-"));

Answer 4

 function myJoin(array, separator=',') { let str = ''; for (let i = 0; i < array.length; i++) { if (array[i] !== null && array[i] !== undefined) str += array[i]; if (i < array.length - 1) str += separator; } return str; } console.log(myJoin(['a','b','c'])); console.log(myJoin(['a','b','c'], '+')); console.log(myJoin(['a',null,'c'], '-')); console.log(myJoin(['a','b',undefined], '.'));

Answer 5

Use default syntax to set the seperator || The a forEach taking in value , index , array Test for last element.

 function myJoin (array, separator) { let newString = ""; separator = separator||','; array.forEach((a,i,arr) => { newString += `${a}${(i < arr.length-1) ? separator : ''}`; }); return newString; } console.log(myJoin(['a', 'b', 'c'], '+')); console.log(myJoin(['a', 'b', 'c'])); console.log(myJoin(['a', 'b', 'c'], '-'));

Answer 6

You can use Array.reduce() to join your array.

 let arr = ['a', 'b', undefined, 'c', 'd', null, 'e']; myJoin = (arr, separator = ',') => arr.reduce((acc, val, i) => acc + ([undefined, null].indexOf(val) >= 0 ? '' : val) + (i < arr.length - 1 ? separator : ''), ""); console.log('myJoin(arr): ', myJoin(arr)); console.log('myJoin(arr, "+"): ', myJoin(arr, '+')); console.log('arr.join("+"): ', arr.join('+'));

Hope this helps,