JavaScript Quirks and notes

JavaScript Quirks and notes

/*********** Checking for not defined / undefined  **********/
foo  
// ReferenceError: foo is not defined

if(foo == null) console.log('this wont work');
// ReferenceError: foo is not defined

if (typeof foo == 'undefined' ) console.log('foo is undef');
// this is the only way to check for not defined


var foo; //define foo, but foo has no value

if (typeof foo == 'undefined' ) console.log('foo is undef');
//this works 

if ( foo == undefined ) console.log('foo is undef');
// this works 


null // used to indicate a deliberate non-value
undefined // used to indicate a value that hasn't been set yet

/////////////////
var test = someObject.methodTest;
test();
//Due to the first case, test now acts like a plain function call; therefore, this inside it will no longer refer to someObject. ie: LHS of test is window object