3

I am using ArrayList as my array,

let ArrayList   =  ['a','b','c','d','e','f'];

I am confused in between Method 1 and Method 2 because in both case I Referenced ArrayList by another you can also check logs over this link https://jsfiddle.net/mnjsnj/u1fms8wx/2/

Method 1

let Method1 = ArrayList;  // Referenced arrayList by another variable 
ArrayList= []; // Empty the array 
console.log(Method1); // Output ['a','b','c','d','e','f']

Method 2

let Method2 = ArrayList;  // Referenced arrayList by another variable 
ArrayList.length = 0; // Empty the array by setting length to 0
console.log(Method2 ); // Output []
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2
  • Initially, both variables reference the same array. Then in the first example a new array is assigned to ArrayList, Method1 is not affected. In the second example, the length of the array that both variables reference is changed. Commented Feb 4, 2019 at 6:10
  • Thank you RobG answer is clear now for me Commented Feb 4, 2019 at 6:18

2 Answers 2

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1

ArrayList is being emptied after first method , so you are assigning an empty array to Method2

let ArrayList = ['a', 'b', 'c', 'd', 'e', 'f'];

let Method1 = ArrayList; // Referenced arrayList by another variable 
ArrayList = []; // Empty the array 
console.log(Method1); // Output ['a','b','c','d','e','f']

console.log('ArrayList after Method1....!' , ArrayList)
// here an empty array is assinged to Method2
let Method2 = ArrayList; // Referenced arrayList by another variable 
ArrayList.length = 0; // Empty the array by setting length to 0
console.log(Method2); // Output []

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1 Comment

Agree with you nice answer thank you
1

The trick to understanding what is going on here is to understand how variables work in JavaScript and what the assignment (=) operator does.

A variable is just a bound name to a memory location.

When we assign something to a variable via the = operator, we only change what that variable is pointing to, we are not changing the actual data at the existing memory location, we're just making the variable not point to it anymore.

// Method1 now points to the same memory location as ArrayList
let Method1 = ArrayList;
// ArrayList variable now points to a new memory location containing an empty array
ArrayList = []; 
// Method1 is still pointing to the original memory location so the array is unaffected
console.log(Method1);

In the second example, you are directly affecting the data at the memory location that ArrayList is pointing to by changing its length to 0.

// point Method2 variable to the same location as ArrayList variable
let Method2 = ArrayList; 
// change the data stored at the location ArrayList is pointing to
ArrayList.length = 0; // Empty the array by setting length to 0
// Since Method2 is also pointing to that location, we see the empty array
console.log(Method2); // Output []
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3 Comments

"In the case of primitives such as strings or numbers, the value is also copied over when a variable is re-assigned so your code would behave as you expect it." Uh? If let ArrayList = 42 and let Method1 = ArrayList; ArrayList = 21;, then Method1 is still 42. Variables always work the same way, it doesn't matter what value they have. Or do you mean something else? I guess I'm confused to which code you are referring to. You also say "since your dealing with an array this works.", so it seems you are saying in both sentences that "it works".
@FelixKling I wrote this answer late at night and half-brained haha I've removed that "feels wrong but unsure how" description
I understand :D

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