Javascript insert array with null value into string - Stack Overflow

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Is there a way to display the null element when concatenated to a string?

var arr = [];
arr.push('x');
arr.push(null);
arr.push('z');

// arr = ['x', null, 'z']

var samp = 'Array elements are: ' + arr;

// Array elements are: 'x',,'z'

Output that I want:

Array elements are: 'x', null,'z'

Is there a way to display the null element when concatenated to a string?

var arr = [];
arr.push('x');
arr.push(null);
arr.push('z');

// arr = ['x', null, 'z']

var samp = 'Array elements are: ' + arr;

// Array elements are: 'x',,'z'

Output that I want:

Array elements are: 'x', null,'z'

• javascript

Share Improve this question Follow asked Aug 7, 2018 at 5:04 DayIsGreenDayIsGreen 26522 gold badges55 silver badges2020 bronze badges 2

• You can concatenate strings only. So check for null if it is null, create null as string "null" and then concatenate. null is a typeof object, so you can do JSON.stringify(null) which will be converted to string – Sivakumar Tadisetti Commented Aug 7, 2018 at 5:06
• @JavascriptLover-SKT - I'm trying to avoid inserting a "null" (as string) into the string as I also need this for SQL Queries where the queries can insert an actual string and an actual null value. – DayIsGreen Commented Aug 7, 2018 at 5:07

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4 Answers 4

Sorted by: Reset to default 10

You can apply String to the arguments using Array.map. It's very succinct:

arr.map(String)

var arr = [];
arr.push('x');
arr.push(null);
arr.push('z');

var samp = 'Array elements are: ' + arr.map(String);
console.log(samp);

Implicitly coercing an array to a string calls the .join method, and:

https://developer.mozilla/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join

If an element is undefined or null, it is converted to the empty string.

So, you can't use implicit coercion or .join. One option would be to use reduce to manually join every element (so as not to skip nulls):

var arr = [];
arr.push('x');
arr.push(null);
arr.push('z');


const joined = arr.reduce((a, elm) => a + (a ? ',' : '') + elm);

var samp = 'Array elements are: ' + joined;
console.log(samp);

If you also want the quotes around each string as with your

Array elements are: 'x', null,'z'

then check the typeof each element before concatenating:

var arr = [];
arr.push('x');
arr.push(null);
arr.push('z');


const joined = arr.reduce((a, elm) => {
  const quote = typeof elm === 'string' ? "'" : '';
  return a + quote + (a ? ',' : '') + elm + quote;
}, '');

var samp = 'Array elements are: ' + joined;
console.log(samp);

(if the elements contain any single-quotes themselves, you may want to replace them with \' as well)

JSON.stringify knows how to represent stuff in string form. If you just stringify your array, you get almost what you want:

JSON.stringify(arr)
# => ["x",null,"z"]

But if you do it yourself, you can avoid the square brackets, put a bit more space in...

arr.map(JSON.stringify).join(', ')
# => "x", null, "z"

That's an unusual yet interesting requirement. The easy thing is that you want to display null as a part of the final string. So, here's what I tried:

function arrToStr(inputArr){ //this func will return str with null
var str=undefined;
inputArr.map(function(i){str = (str!==undefined) ? (str+", "+i) : i})
return str;
}

var arr = [];
arr.push('x');
arr.push(null);
arr.push('z');

var samp = 'Array elements are: ' + arrToStr(arr);
//samp - "Array elements are: x, null, z"

Hope you got the catch here?

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