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From ES6:

On es2pi:

Type Checkers

  • Function.isFunction( unknown )
  • Function.prototype.classOf()
  • Function.prototype.typeOf()
  • Function.prototype.isFunction()

Function.isBuiltIn( unknown )


Checks if the function is built-in. False if the function is defined in JavaScript. Handy to check if the function is polyfilled.


Function.toMethod( fun )

Converts the function fun to a method, which is a function that takes this as the first argument of the original.

String.prototype.to_i = Function.toMethod(parseInt);
"42.195".to_i(); // 42


Converts the method to a function whose first argument is bound to this in the original method.

var has = ({}).hasOwnProperty.toFunction();
has({}, 'hasOwnProperty');                // false
has(Object.prototype, 'hasOwnProperty');  // true

Function.prototype.memoize( [ toStr, memo ] )

Turns the function into a memoized version. The resulting function first looks up the memo for the argument and if found, returns it. The original function is invoked iff the argument is not found and upon return the result is cached in the memo.

 var fib = function(n){
    return n < 2 ? n : fib(n - 1) + fib(n - 2) 


The optional first argument is a function that turns the argument into the key string. Default is the identity function (function(a){return a}).

The second argument is an object used for memo. By default it is automatically created internally via Object.create(null).

See Also:

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