I want to create array once and then just push values to it with any index , but i get Cannot read property 'push' of undefined error
I have following scenario
var neg = [];
I want to use push randomly with any index
neg[0].push([1,2]);
or
neg[22].push([1,2]);
right now I want to define manually like neg[0] = []; , Is there any one way where i can just push to any index i want ?
Here's a quick way to do exactly what you want.
var arr = [];
(arr[0]=[]).push([1,2]);
console.log(arr)Also it's safer to check if an array already exists at this index, otherwise it will be replaced with an empty array – the above code will replace the array with an empty one if it already exists.
// creates an array at index 0 only if there's no array at this index.
// pushes an array of [1, 2] to the existing array at 0 index
// or the newly created empty one.
(arr[0] || (arr[0] = [])).push([1, 2]);;
var arr = [];
arr[0] = [1];
(arr[0]||(arr[0]=[])).push(2,3);
console.log(arr)You are going to have to set it to an empty array before you can push it.
neg[0] = neg[0] || []
neg[0].push([1,2]);
Push will add elements to the end of an array. For example:
var neg = [];
neg.push(3); //this will add the number 3 to the end of your array
The problem here is your trying to add a value to an undefined element:
var neg = [];
neg[0].push([1,2]); // <-- neg[0] is not defined at this moment, and you're treating it as an array object.
If you define your elements as an array, you will not get such an error:
var neg = [];
neg[0] = [];
neg[22] = [];
neg[0].push([1,2]);
neg[22].push([1,2]);
Alternatively (and this is probably what you're probably looking for), you can set the value for any element of your array with the desired index:
var neg = [];
neg[0] = [1,2];
neg[22] = [1,2];
You can specify how large the array will be if you know ahead of time, for example var neg = new Array(40); will create a new array with 40 undefined elements.
Once that is created, you can change the value at any index as long as 0 <= index <= 39.
var myArray=[]). Also, note that push will add elements to the end of the array (even beyond it's initial length) and returns the new length of the array --example here: jsbin.com/nuriqiqixa/edit?html,js,console,output
var neg = [40] creates an array with one item with the value 40 not an array with 40 items.You can use array.splice(your_index, 0, your_element); to push an element into an array at the given index.
neg[0]is not an array, so your trying to effectively push something onto an undefined valueneghave a fixed size?