Random JS quirks, tricks, tips, and hacks.

js.js

/*
* Disclaimer: I neither endorse nor necessarily support these techniques. In general, I value readability over brevity, but I found
* some of these to be somewhat interesting and worth noting and sharing, as I have seen them used extensively.
*/


/* Convert any value to a Boolean */
var myVal = null;
!!myVal; // false

myVal = 0;
!!myVal; // false
myVal = 1;
!!myVal; // true
myVal = 2;
!!myVal; // true



/* Convert the result of an indexOf to a Boolean representing whether or not the item was found */
var myArr = [1, 2, 3];
~myArr.indexOf(1); // -1
~myArr.indexOf(2); // -2
~myArr.indexOf(3); // -3
~myArr.indexOf(4); // 0

// Note that the result of ~ is effectively -(x + 1)

// All together now...
!!~myArr.indexOf(1); // true
!!~myArr.indexOf(2); // true
!!~myArr.indexOf(3); // true
!!~myArr.indexOf(4); // false

// Setting default values 
function myFunction (myParam) {
  myParam = myParam || 'my default string';
  return myParam;
}
myFunction(); // 'my default string'

// Note that this will set the default value for all falsy values
myFunction(0); // 'my default string'
myFunction(null); // 'my default string'
myFunction(false); // 'my default string'



/* Simultaneously checking for null and undefined */
var myUndefinedVal,
  myNullVal = null;
  
myUndefinedVal == null; // true
myNullVal == null; // true



/* Multiple ways to assign a conditional value */
var myConditional = Math.floor(Math.random()*2), // either 0 or 1
  myConditionalValue;

// Standard if/else
if (myConditional) {
  myConditionalValue = 'yes';
} else {
  myConditionalValue = 'no';
}

// Ternary
myConditionalValue = myConditional ? 'yes' : 'no';

// Logical AND
myConditionalValue = myConditional && 'yes'; // this only works if you want a falsy value for the failure condition of the conditional

// Switch
switch (myConditional) {
  case 1:
    myConditionalValue = 'yes';
    break;
  case 0: // or default
    myConditionalValue = 'no';
    break;
}



/* Early-exit conditions */

// Standard function
function myStandardFunction (myParam) {
  if (myParam) {
    // do something with a truthy myParam value
  }
}

// Short-circuiting function
function myEfficientFunction (myParam) {
  if (!myParam) return;
  
  // do something with a truthy myParam value
}