Javascript Updating Global Object inside a function

Question

I see my global variable which is an object is getting modified inside a function.

Below is the example I created:

var globalVarForTest = ["dfbsdfbsdfb", "sfgb", "gtsgt", "ttt"];

function testingError() {

  console.log("BEFORE")
  console.log(globalVarForTest);
  for (var i = 0; i < globalVarForTest.length; i++) {
    console.log(globalVarForTest[i]);
  }


  //Modifying Local Variable
  var localVarforTest = globalVarForTest;
  for (var i = 0; i < localVarforTest.length; i++) {
    localVarforTest[i] = localVarforTest[i].length;
  }




  console.log("AFTER")
  console.log(globalVarForTest);
  for (var i = 0; i < globalVarForTest.length; i++) {
    console.log(globalVarForTest[i]);
  }

}

testingError();

The function prints BEFORE and AFTER different values for a global variable.

How to set a local variable inside a function equal to a global array so that the global array is not modified in the function?

marvel308 · Accepted Answer · 2017-08-22 13:07:37Z

1

You would have to clone it without reference.

var globalVarForTest = ["dfbsdfbsdfb","sfgb","gtsgt","ttt"];

var temp = globalVarForTest.slice(0);

console.log(temp);
temp.push('temp');
console.log(temp);
console.log(globalVarForTest);

answered Aug 22, 2017 at 13:07

marvel308

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Comments

Kresimir Pendic · Accepted Answer · 2017-08-22 13:15:38Z

you can use JSON native parse method to convert from and to obj..

var globalVarForTest = ["dfbsdfbsdfb","sfgb","gtsgt","ttt"];

            function testingError(){

            console.log("BEFORE")
            console.log( globalVarForTest );
            for( var i=0; i<globalVarForTest.length; i++ ){
                    console.log( globalVarForTest[i]);
            }


              //Modifying Local Variable
            var localVarforTest = JSON.parse(JSON.stringify( globalVarForTest ));
            console.log( localVarforTest );
            for( var i=0; i< localVarforTest.length; i++ ){
                    console.log( localVarforTest[i]);
            }


            console.log("AFTER");
            console.log( globalVarForTest );
            for( var i=0; i<globalVarForTest.length; i++ ){
                    console.log( globalVarForTest[i]);
            }


            }

testingError();

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