delete in javascript

標籤：

Key word delete.

1. Delete global object.

x = 42;         // creates the property x on the global objectvar y = 43;     // creates the property y on the global object, and marks it as non-configurablemyobj = {  h: 4,  k: 5};// x is a property of the global object and can be deleteddelete x;       // returns true// y is not configurable, so it cannot be deleted                delete y;       // returns false // delete doesn‘t affect certain predefined propertiesdelete Math.PI; // returns false // user-defined properties can be deleteddelete myobj.h; // returns true // myobj is a property of the global object, not a variable,// so it can be deleteddelete myobj;   // returns truefunction f() {  var z = 44;  // delete doesn‘t affect local variable names  delete z;     // returns false}

 

2. Function

function Foo(){}Foo.prototype.bar = 42;var foo = new Foo();// returns true, but with no effect, // since bar is an inherited propertydelete foo.bar;           // logs 42, property still inheritedconsole.log(foo.bar);// deletes property on prototypedelete Foo.prototype.bar; // logs "undefined", property no longer inheritedconsole.log(foo.bar);

 

3. Array

var trees = ["redwood","bay","cedar","oak","maple"];delete trees[3];if (3 in trees) {    // this does not get executed}var trees = ["redwood","bay","cedar","oak","maple"];trees[3] = undefined;if (3 in trees) {    // this gets executed}

 

delete in javascript