1. Get Integer Part
Firstly, the classic ways:
// Math.floor() works for positive only
Math.floor(-1.2); // -1
// Math.ceil() works for negative only
Math.ceil(1.3); // 2
// Math.round() works fine
Math.round(1.2); // 1
Math.round(-1.2); // -1
// ParseInt()
parseInt(1.2, 10); // 1
parseInt(-1.2, 10); //-1
Then, tricks probably won't help you pass the code review:
~~1.1 // 1
~~1.8 // 1
~~(-1.1) // -1
~~(-1.8) // -1
~~-1.1 // -1
const three = ~~(10/3);
// another trick
console.log(1.2 | 0); // 2
console.log(-1.2 | 0); // -1
// another way using bit
1.2>>0 // 1
-1.2>>0 // -2
The reason bit works is that internally, bit operation is like:
- convert the number from double-float to int
- then do bit operations, |(or), ~(revert) etc
- then convert back to float
2. Get Boolean
// using !!
!!5 // true
!!true // true
!!'' // false
!!null // false
!![] // true
3. Odd, Even
function isOdd(n) {
return !!(n & 1);
}
isOdd(12); // false
isOdd(1); // true
// Pay attention that following returns 0
12 & 1 === 0 // 0, instead of true
(12 & 1) === 0 // true
4.How to detect a variable is declared or not?
We know that if we reference an none-exists key inside a object, it returns undefined.
const obj = {};
obj.noneExist; // undefined
And we also know that if we are trying to access an variable that is not defined, it returns an error:
let newValue = oldValNotExist;
// Uncaught ReferenceError: oldValNotExist is not defined...
So, question is, how to tell if oldValNotExist exist or not without throwing any error?
// use typeof
if (typeof oldValNotExist !== 'undefined') { ... }
// no error will be thrown
// btw, dont forget this:
typeof null === 'object' // true
Ref.: http://bonsaiden.github.io/JavaScript-Garden/#function.arguments