V8 and Javascript gotchas

 Gotcha #1: this keyword

Gotcha #2: variable scope and variable evaluation strategy

 Object properties are not iterated in order (V8)

 Comparing NaN with anything (even NaN) is always false

console.log("Inputis 123 - ", !isNaN(parseInt("123", 10)));

console.log("Inputis abc - ", !isNaN(parseInt("abc", 10)));

 

Floating point precision

console.log(0.1 + 0.2); // 0.30000000000000004

console.log(0.1 + 0.2 == 0.3); // false

 

Functions are objects, so they can have properties attached to them.

function doSomething() { return doSomething.value + 50; }
var doSomethingElse = function() { return doSomethingElse.value + 100;};
doSomething.value = 100;
doSomethingElse.value = 100;
console.log( doSomething() );
console.log( doSomethingElse() );

1. LOG 150
2. LOG 200

The arguments variable available in functions is
not an Array, through it acts mostly like an array. For example, it does not have the push() and pop() methods but it does
have a length property

 

To create an array from the arguments property, you can use Array.prototype combined with Function.call:

 

function test() {

  // Create a new array from the contents of arguments

  var args =Array.prototype.slice.call(arguments); // returns an array

  console.log(args.length);

  console.log(args.concat(['a', 'b', 'c'])); //works

}

test(1,2, 3);

1. LOG 3

1. LOG [1,2,3,"a","b","c"]

function a(){console.log(arguments.callee)}

a()

functiona(){console.log(arguments.callee)}

 

function a(){console.log(arguments.caller)}

a()

undefined

 

function a(){console.log(a.caller)}

a()

functioneval() { [native code] }

 

function a(){console.log(a.callee)}

a()

undefined

 

 

myfunc.apply(obj,arguments).

 

// concat arguments onto the

Array.prototype.concat.apply([1,2,3],arguments).

 

// turn arguments intoa true array

var args =Array.prototype.slice.call(arguments);

 

// cut out first argument

args =Array.prototype.slice.call(arguments, 1);