Javascript pushing objects into array - Stack Overflow

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var cb = [];
for (var i = 0; i < 10; i++) {
    cb.push({
        'test': 'value'
    });
    console.log(cb);
};

I'm expecting to get: [{test: value}, {test: value}, ... , {test: value}]

What I end up getting is the final result at every log statement:

[Object]

[Object, Object]

[Object, Object, Object]

[Object, Object, Object, Object]

[Object, Object, Object, Object, Object]

[Object, Object, Object, Object, Object]

[Object, Object, Object, Object, Object, Object]

..........

When I expand any of those arrays they all have the same result. For example, the first array contains:

[{test: value}, {test: value}, ... , {test: value}] 

which is the final value, shouldn't it just have 1 object? The final result is what I expect, but I'm just confused about why after the first push the array has 10 elements. Can someone please explain what's going on?

var cb = [];
for (var i = 0; i < 10; i++) {
    cb.push({
        'test': 'value'
    });
    console.log(cb);
};

I'm expecting to get: [{test: value}, {test: value}, ... , {test: value}]

What I end up getting is the final result at every log statement:

[Object]

[Object, Object]

[Object, Object, Object]

[Object, Object, Object, Object]

[Object, Object, Object, Object, Object]

[Object, Object, Object, Object, Object]

[Object, Object, Object, Object, Object, Object]

..........

When I expand any of those arrays they all have the same result. For example, the first array contains:

[{test: value}, {test: value}, ... , {test: value}] 

which is the final value, shouldn't it just have 1 object? The final result is what I expect, but I'm just confused about why after the first push the array has 10 elements. Can someone please explain what's going on?

• javascript

Share Improve this question Follow edited Mar 9, 2016 at 17:23 Mike Cluck 32.5k1313 gold badges8383 silver badges9494 bronze badges asked Mar 9, 2016 at 17:19 Milan DimicMilan Dimic 2311 gold badge33 silver badges66 bronze badges 4

• 2 console.log shows the state of cb now, and not at the time it was logged. – Siguza Commented Mar 9, 2016 at 17:21
• Possible dublicate: stackoverflow./questions/750486/… – Bjørn Sørensen Commented Mar 9, 2016 at 17:21
• 2 Try doing console.log(JSON.stringify(cb)) and you'll see what @Siguza is saying. Or even console.log(cb.length) will show you that the length is increasing correctly. – Mike Cluck Commented Mar 9, 2016 at 17:22
• The log does not show the exact state of an array/object when you log it. stackoverflow./questions/4057440/… – epascarello Commented Mar 9, 2016 at 17:37

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 3

You need to serialize yor output. Try:

var cb = [];
for (var i = 0; i < 10; i++) {
    cb.push({
        'test': 'value'
    });
    console.log(JSON.stringify(cb));
};

You are logging the array object, not any aspects of the object. The output is correct and so is the array. You just need to be more specific. If you set a breakpoint into the code where your console.log line is, you'll see that the array is being populated correctly.

And, if you don't want to see the object's state as it's being built, just move the log outside of the loop.

Doing cb[test]="value" (or maybe cb[myObject]="value"? I'm not sure what you want) would have returned what you expected : an array whose only key test (or myObject) contains the defined value.

When using push instead, you use the array not as an associative array (key = value) but rather as an indexed array (index = value), and push's contract is to add to the end of the array, using the next available index.
So now cb[0] is {test: "value"} and so are the others cb[1] to cb[9].

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