CODEWITHSUNDEEP
javascriptarraysobjectjavascript-objects
FlowLess10
FlowLess10

Reputation: 133

Object gets changed even if I do not make any operations with it

Can someone tell me why in the following code snippet the value of ColumnNames is changed at the position of the debugger? It takes the same value as tempColumns after tempColumns[k] = modi[i].data[k];. 

var addRecords= []; 
var columns = ["Column1","Column2","Column4","Column5"]
var columnNames = {};
var modi = [{
 data: {
  Column1: 'bla'
 }
},{
 data:{
  Column2: 'test'
 }
}];
var tempColumns = {};

for( var n in columns){
 var column = columns[n];
 columnNames[column] = "";
}

for(var i in modi){
 tempColumns = columnNames;
 for(var k in modi[i].data){
  tempColumns[k] = modi[i].data[k];
  debugger;
 }
 addRecords.push(tempColumns);
}

Upvotes: 0

Views: 95

Answers (2)

DropMania
DropMania

Reputation: 133

You need to make a copy of the object. When you say tempColumns = columnNames then they both point to the same memory. with the following method you can make a copy from an object: JSON.parse(JSON.stringify(obj))

obj = {1:"hi", 2:"by"};

newobj = JSON.parse(JSON.stringify(obj));
newobj["1"] = "hello";

console.log(obj);
console.log(newobj);

Upvotes: 1

Guts
Guts

Reputation: 768

It is happening because you assigned columnNames to tempColumns before your debugger. In javascript values of objects are passed by reference which means that after line:

tempColumns = columnNames

tempColumns and columnNames point to the same position in memory.

Upvotes: 4

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