Xah Web Dev Blog Archive 2015-09

2015-09-30

JavaScript quiz of the day. true or false?

function f () {};
Function.prototype = 3;
console.log( f instanceof Function );

refresh here instanceof Operator, but that still may not answer why.

puzzling? discuss at ~~https://plus.google.com/+XahLee/posts/CLMxi9LGteG~~

Solution

this will silently fail.

// silently fail
Function.prototype = 3;

If you add "use strict", then error is reported.

"use strict";
Function.prototype = 3;

// Function.prototype = 3;
//                    ^
// TypeError: Cannot assign to read only property 'prototype' of function Function() { [native code] }

You cannot change Function.prototype, because the “prototype” property there does not have “writable” attribute.

console.log(
 Object.getOwnPropertyDescriptor(Function,"prototype")
);

// output:
// { value: [Function: Empty],
//   writable: false,
//   enumerable: false,
//   configurable: false }

Property Attributes

2015-09-28

HTML: Input Range Slider

2015-09-27

SVG Clock (updated. Using svg transform instead for moving the hands.) [see SVG: Coordinate Transformation]

2015-09-25