CODEWITHSUNDEEP
javascriptjquery
Mina Gabriel
Mina Gabriel

Reputation: 25110

How can i execute a function while creating an object using javascript?

How can i execute a function while creating an object using javascript

Running the following code 

 var y = [] ;
 var x = [[1,2,3] , [4,5,6] , [7,8,9]]
 for (var i = 0 ; i < 3 ; i++){
     y.push({name :'MyName' , value:function(){return x[i]} }) ; 
 }

 console.log(y) ;

will generate the following object 

{name : 'MyName' , value : function (){return x[i]}

Question

how can i execute this object function having this : 

{name : 'MyName' , value : function (){return [1,2,3]}

i tried eval() it didn't work

Here is my jsFiddle

For the people who ask WHY are you doing this ? I'm doing this because object will be copied by value so i will end up having all me object.Value equal to X[2] ;

Upvotes: 2

Views: 158

Answers (2)

si_bromley
si_bromley

Reputation: 1

To successfully add those objects to the array you need to create a closure over the y.push() statement. The closure will ensure the variable x[i] will be available to the value() function when it is invoked.

The code below defines the 'addItem()' function which closes over the 'value()' function of the object creating a self contained environment. This means the 'value()' function will still have access to the variables defined or passed within the 'addItem()' function even after the 'addItem()' function has finished.

var i = 0
var y = [] ;
var x = [[1,2,3] , [4,5,6] , [7,8,9]];

function addItem(item) {
    y.push({
        name: 'MyName', 
        value: function () {
            return item;
        }
    });
}

for ( ; i < 3 ; i++) {
    addItem(x[i]);
}

console.log(y);
/*
[ { name: 'MyName', value: [Function] },
  { name: 'MyName', value: [Function] },
  { name: 'MyName', value: [Function] } ]
*/
console.log(y[0].value()); // [1, 2, 3]
console.log(y[1].value()); // [4, 5, 6]
console.log(y[2].value()); // [7, 8, 9]

You can also achieve the same thing using an anonymous function within the loop but I choose not to do this as that would have created a new function each time you went around the for loop.

Upvotes: 0

David
David

Reputation: 8660

Its an odd bit of code. Im not sure what you are trying to achieve. But the problem you are having is that i is being incremented throughout the loop. So when eventually you call the function the value for i is 3 and so beyond the bounds of the x array. You could fix it like this:

var y = [] ;
var x = [[1,2,3] , [4,5,6] , [7,8,9]]
for (var i = 0 ; i < 3 ; i++){
    y.push({
        name :'MyName',
        index: i,
        value:function(){return x[this.index]; } 
    }) ; 
}

console.log(y[0].value());

Or if you do not explicitly need a function to execute:

var y = [] ;
var x = [[1,2,3] , [4,5,6] , [7,8,9]]
for (var i = 0 ; i < 3 ; i++){
    y.push({
        name :'MyName',
        value: x[i]
    }) ; 
}

console.log(y[0].value);

Upvotes: 2

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