How can I add an array into another array in Javascript?

Question

I have an two element array looking like this

headers = [{x: 1, y: 2},{x: 2, y: 3}]

I have another three element array that looks like:

ans = [{r: true},{r: false},{r:true}]

How can I add the second array to the first row of the first array to give:

[{x: 1, y: 2, ans: [{r: true},{r: false},{r:true}] },{x: 2, y: 3}]

Note that I don't want to define ans beforehand as it could be an array or something else. Also sorry but I think my representation of the array might not be quite the correct syntax. Hope it makes sense.

• user1636522: "Cannot set property 'ans' of undefined" is different than "ans is undefined". Which one of these errors is raised?

Answer 1

You actually want to add another property to an element in an array. You can do it like this

 headers[0].ans = ans;

• Samantha J T Star: Sorry for the repeated same comment but headers[0] is an object with fields. When I try the above it says "ans is undefined".

Answer 2

You could do something like this...

var headers = [{x: 1, y: 2},{x: 2, y: 3}];
var ans = [{r: true},{r: false},{r:true}];
// define what you want the newly added property to be called
var collectionName = "ans";
// assign it only to the first item in the headers array
headers[0][collectionName] = ans;
// here are your results
console.log(JSON.stringify(headers));

here is a working fiddle that will output the array for you to look at in an output div

http://jsfiddle.net/9KR2P/

• Samantha J T Star: This still gave me: Cannot set property 'ans' of undefined
• Stephen James: @SamanthaJ take a look at the working fiddle link which I've added in an edit.
• Samantha J T Star: Thanks. I will look at this now. I am having some trouble getting internet now. Did you see the other answer and fiddle. It's different from yours. Just wonder which is best. Right now I cannot get fiddle to come up but hopefully soon.
• Stephen James: its different because its using dot notation to reference the property, which is good - my example uses [] to reference the property so that we can change the property name of "ans" in the target object to whatever you want it to be. I just put in more code to illustrate that really.

Answer 3

Simply assign your property to your object : headers[0].ans = ans

• Samantha J T Star: I tried this but headers[0] is an object with fields. When I try the above it says "ans is undefined".

Answer 4

var headers = [{x: 1, y: 2},{x: 2, y: 3}],
 ans = [{r: true},{r: false},{r:true}];
headers[0].ans = ans;

• Samantha J T Star: Jon - I tried this but headers[0] is an object with fields. When I try the above it says "ans is undefined".