Page 196 - JavaScript

'T'
'F'

Example 2

F() && T(); // false

Output:

'F'

Example 3

T() || F(); // true

Output:

'T'

Example 4

F() || T(); // true

Output:

'F'
'T'

Short-circuiting to prevent errors

var obj; // object has value of undefined
if(obj.property){ }// TypeError: Cannot read property 'property' of undefined
if(obj.property && obj !== undefined){}// Line A TypeError: Cannot read property 'property' of
undefined

Line A: if you reverse the order the first conditional statement will prevent the error on the second
by not executing it if it would throw the error

if(obj !== undefined && obj.property){}; // no error thrown

But should only be used if you expect undefined

if(typeof obj === "object" && obj.property){}; // safe option but slower

Short-circuiting to provide a default value

The || operator can be used to select either a "truthy" value, or the default value.

https://riptutorial.com/ 153