By ‘reference’ and by ‘value’

By Reference: with Objects (incl. functions)


var a, b;
var a = { myObj: "value" };
b = a;
// b points to same location in memory
console.log(a); // Output: Object {myObj: "value"}
console.log(b); // Output: Object {myObj: "value"}
// EXCEPT when you create a new object with equals operator
var a = { myObj: "value2" };
console.log(a); // Output: Object {myObj: "value2"}

var a, b;

var a = { myObj: "value" };

b = a;

// b points to same location in memory

console.log(a); // Output: Object {myObj: "value"}

console.log(b); // Output: Object {myObj: "value"}

// EXCEPT when you create a new object with equals operator

var a = { myObj: "value2" };

console.log(a); // Output: Object {myObj: "value2"}

By Value: with primitive types


var a = true;
var b;
var b = a;
//b is now a COPY of a - a new value so 
console.log(a === b); // <- true

var a = true;

var b;

var b = a;

//b is now a COPY of a - a new value so

console.log(a === b); // <- true

Peter Dillon

Development teams seek me out for visual design, reskinning, information hierarchy, usability, iconography, improving task flow, improving the front end build process and more. I specialize in creating engaging solutions to solve real world problems while designing beautiful applications that make the lives of users easier.