for..in is used to iterate through the properties in our javascript objects.
The syntax
for (variable in object) { //do something with the variable }
Example
"use strict" var obj = {a:1, b:2, c:3}; for (var prop in obj) { console.log("obj." + prop + " = " + obj[prop]); } // Output: // "obj.a = 1" // "obj.b = 2" // "obj.c = 3"
You may also use the for..in without using the var keyword if you do no have “use strict” at the top.