I was browsing through some code and I was wondering how this could be useful
grid.push([].concat(row));
In my understanding it is the same as
grid.push([row]);
Why the 'concat' fuss?
4 Answers
You want to use .concat when you need to flatten the array and not have an array consisting of other arrays. E.g.
var a = [1,2,3];
var b = [4];
Scenario 1
console.log(b.push(a));
// Result: [4, [1,2,3]]
Scenario 2
console.log(b.concat(a));
// Result: [4,1,2,3]
So both of your scenarios in an array of array. Since [].concat() results in an array only, pushing both [row], [].concat(row) has the same result.
But if you want a flattened array, there is a slight change needed in your code, that you have to .concat the array row with grid and not .push the result of concat to it, as shown in scenario 2
5 Comments
Rayon
console.log(b.push([a]));... (grid.push([row]);). It is how OP has specified in post.. I am curious about the difference...Rayon
Both will produce array of an array...Better to provide executable snippet with valid syntax as provided in question...
Aditya Singh
By both do you mean
b.concat(a) and b.push(a) or the ones referred in OPs question?Rayon
We are dealing with the code OP has provided right ? I am not concerned with the code provided in your answer..
Aditya Singh
Ok. On second glance I got what you were telling. Let me updated the answer
Check my variant:
let arr = [];
let tmp = [ 1, 2, '300$' ];
arr.push(...tmp);
Comments
var canEmptyArray = [];
grid = [...(grid), ...(canEmptyArray), ...(row)];
All arrays can be empty as long as it is in the array format
Comments
With grid.push([row]); you are pushing an array containing the row itself. If row is an array (e.g. [0, 1, 2]). You will push an array containing another array (i.e. [[0, 1, 2]]).
With grid.push([].concat(row));, you are pushing an array containing the elements contained in row (i.e. [0, 1, 2]).
However it is unclear why it is not just written grid.push(row) which, if row is an array, could seem more or less the same as grid.push([].concat(row));.
I can find two explanations for this:
rowis not an array but an "array-like" object and[].concat(row)is used to convert it (just likeArray.fromcould do).Your coder does not want to push
rowbut a copy of row instead that protected against any further modification of the originalrow.
rowmight be a primitive (or simply not an array) value.