var arr = [] var index = 0 var postfix = 0 for (; index < 10; index++) { postfix = 0 console.log(postfix) // 0 0 0 0 0 0 0 0 0 0 for (; postfix < 100; postfix++) { arr.push(index * 100 + postfix) } } console.log(arr, arr.length) // ... 1000 arr = [] index = 0 postfix = 0 for (; index < 10; index++) { console.log(postfix) // 0 100 100 100 100 100 100 100 100 100 for (; postfix < 100; postfix++) { arr.push(index * 100 + postfix) } } console.log(arr, arr.length) // ... 100