Javascript Patterns Book

Question 1

How does javascript read statements, right to left or left to right?

Answer 1

Right to left. 
var x = y = 10; // beware of the possible global variable y

Question 2

Why is it faster for for-loops to count down to zero than up to max?

Answer 2

It’s faster to compare against zero than anything else.

Question 3

How can you protect against naming collisions with the hasOwnProperty method? (e.g. make sure a method of that name isn’t added to your object)?

Answer 3

Create a shortcut to it:
var hasOwn = Object.prototype.hasOwnProperty;
Then say: hasOwn.call( myObj, "myProp" );

Question 4

If augmenting a built-in function (which should only be done for purpose of polyfill) how should you check that the polyfill is needed?

Answer 4

if ( typeof Object.prototype.polyfillMethod !== "function" ) {
   // make the method

Question 5

What is right way to use parseInt() function?

Answer 5

parseInt( num, radix ); use radix to avoid confusion. E.g. parseInt( ‘09’ ) will be 0 in ES3 because it assume octal number.

Question 6

What is currying?

Answer 6

The process of making a function able to understand and handle partial application.
Partial application: passing just some and not all arguments to a function.

Question 7

How do you make a generic curry function?

Answer 7

function (fn) {
    var storedArgs = Array.prototype.slice.call( arguments, 1);
    return function( ) {
        var newArgs = A.p.slice.call( arguments ),
    allArgs = storedArgs.concat(newArgs);
return fn.apply( null, allArgs );

Question 8

What are two reasons to use object literal not object constructor

Answer 8

Scope resolution will be more involved with constructor because js will need to make sure you aren’t using a local Object. Also, unexpected results with new Object( 5 ) or new Object ( true )

Question 9

What gets returned from a constructor?

Answer 9

The object referred to by ‘this’ (default) or another object. Must be an object though. This is used by jQuery so you can say new or not — either way, a new unit obj is returned

Question 10

What does it mean to throw an error as a literal?

Answer 10

It means not using new Error() constructor. Just say throw Error( ) or throw { message: "something",  remedy: someFunc }
Advantage is you can set custom parameters.