CODEWITHSUNDEEP
javascriptarrayssorting
htoniv
htoniv

Reputation: 1668

Getting unexpected result while sorting with null in JavaScript

I have an array that contains values like this:

var testSorting = [0,null,1,0,1,null];

When I sort it like this:

testSorting.sort()

then the output is [0, 0, 1, 1, null, null]

But if I do it like this:

testSorting.sort(function(a, b){
    return a-b;
});
console.log(testSorting);

the output is [0, null, 0, null, 1, 1].

I don't know why the result is like this. I need the result to be like the first method.

Upvotes: 3

Views: 70

Answers (1)

user1106925
user1106925

Reputation:

null coerces to 0 in math operations and to a string "null" in .toString() operation, which is what happens when you don't provide a callback.

So in the first code, it's as though you're sorting this:

['0','null','1','0','1','null']

And in the second, it's as though you're sorting this:

[0,0,1,0,1,0];

If you need it to be like the first, then you need to make sure that the a===null values always return a value higher than the other numbers and the b===null values always return one lower.

var testSorting = [0,null,1,0,1,null];

testSorting.sort(function(a, b){
    return a === null ? Infinity :
           b === null ? -Infinity :
                        a - b;
});
document.querySelector("pre").textContent = JSON.stringify(testSorting, 2, null);
<pre></pre>

Upvotes: 2

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