A little more javascript
Last update: 2016/4/4
// Javascript code blocks
//
// Author: ch3cooh
//
// !!! BUG ALERT !!!
// To oschina.net:
// A single quote inside line comment will cause the syntax highlighting to fail :(
// print a split line on the screen
function title_line(title)
{
var len = 78;
title = title || '';
var head_len = Math.floor((len - title.length)/2);
var s = '';
for(var i=0; i<head_len; i++) {
s += '-';
}
s += title;
for(var i=0; i<len-head_len-title.length; i++) {
s += '-';
}
console.log(s);
}
// dollar sign can be used in variable names in javascript
(function (){
title_line('use $ as a variable name')
var $ = 'money';
var $$ = 'more money';
var $$$;
console.log($);
console.log($$);
console.log($$$);
})();
// one way to make an array in javascript
(function () {
title_line('define an array in js');
var list = new Array(10);
list[2] = 'bonjour';
console.log('length of the list is', list.length);
console.log('content of this list:');
for(var i=0; i<list.length; i++) {
console.log("list[", i, "] = ", list[i]);
}
})();
// Question: Is there for-each in javascript?
(function () {
title_line('another way to define an array');
var list = ['un', 'deux', 'trois', 'quatre', 'cinq'];
for(var i=0; i<list.length; i++) {
console.log(list[i]);
}
})();
// Redeclaration of a variable does not change its original value
(function() {
title_line('declare a variable twice');
var old = 'long time ago';
console.log(old);
var old;
console.log(old);
})();
// Declare a variable using new
(function() {
title_line('declare with new');
var num = new Number; // here hum is initialized!
console.log(typeof num, '---', num);
num = "je ne suis pa un nombre";
console.log(typeof num, '---', num);
})();
// build an object in javascript
(function() {
title_line('object == dictionary?');
var study_master = {
'name':'gpa_guru',
'gpa':4.3,
'study' : function () {
this.gpa+=0.1;
},
'bluff' : function () {
console.log('My gpa is as low as', Math.min(this.gpa-1.0, this.gpa));
},
'talk' : function () {
console.log('Bonjour! je suis', this.name, '!')
}
};
study_master.talk();
study_master.bluff();
study_master.study();
study_master.bluff();
console.log(typeof study_master);
})();
// try-catch-throw
(function() {
title_line('try-catch-throw');
try {
try {
foo();
}
catch(err) {
console.log(typeof err, '---', err);
throw 'not in a good mood today';
}
}
catch(err) {
console.log(typeof err, '---', err);
}
})();
// define an object
(function() {
title_line('several ways to define an object');
var o1 = {'233':'lol'};
console.log(o1['233']);
console.log(o1[233]);
console.log(o1[666]); // undefined
var o2 = {name: 'Richard Feynmann'};
console.log(o2.name);
// 2 ways to access the properties of an object:
// a. bracket notation: obj['name']
// b. dot notation: obj.name
})();
// null and undefined
(function() {
title_line('null and undefined');
var nothing;
console.log(typeof nothing, '---', nothing);
var nothing = null;
console.log(typeof nothing, '---', nothing);
var nothing = {};
console.log(typeof nothing, '---', nothing);
})();
// create an object using function
(function() {
title_line('another way to define an object');
function Student(name, age, gender, major) {
this.name = name || 'unknown';
this.age = age || 'unknown';
this.gender = gender || 'secret';
this.major = major || 'no decided yet';
this.sayhi = function () {
console.log('Bonjour! Je suis', this.name,'!');
}
}
var tom = new Student('tom');
tom.sayhi();
})();
// what is in this
(function() {
title_line('this variable');
var property_count = 0;
var method_count = 0;
console.log('These are the properties and methods of this:');
for(var p in this) {
console.log(p);
if(typeof this[p] == 'function') {
method_count++;
} else {
property_count++;
}
}
console.log(method_count + " methods and " + property_count + ' properties in total');
})();
// a helper function to display all the fields and methods of a object
function inspect(obj) {
var info = '';
for(var p in obj) {
info += '[' + typeof obj[p] + '] ' + p + ' : ' + obj[p] + '\n';
}
return info;
}
(function() {
title_line('object again');
function Person(name) {
this.name = name;
}
var tom = new Person('tom');
console.log(typeof tom);
console.log(inspect(tom)); // strangely 'constructor' is not displayed
console.log(tom.constructor);
})();
(function () {
title_line('instanceof operator');
function quick_eval(str) {
console.log (str + ' --> ' + eval(str));
}
quick_eval('233 instanceof Object');
quick_eval('console.log instanceof Function');
quick_eval('"bonjour" instanceof Object');
quick_eval('666 instanceof Number');
quick_eval('new Number(3.14) instanceof Number');
quick_eval('new String("naive") instanceof Object');
quick_eval('String(233) instanceof Object');
// typeof String(233) ---> 'string'
// typeof new String(233) ---> 'object'
})();
(function() {
title_line('strange behavior of constructor');
var o1 = new (function() {
// var this;``-- the compiler is doing such thing
this.name = 'some stupid object';
// return this;
})();
console.log(typeof o1);
console.log(o1.constructor);
console.log(o1.name);
var o2 = new (function() {
this.name = 'another stupid object';
return {
'name': 'not that stupid'
};
})();
console.log(typeof o2);
console.log(o2.name);
console.log(o2.constructor);
var o3 = new (function() {
this.name = 'still an stupid object';
return 233;
})();
console.log(o3.name);
})();
// built-in objects in javascript
// Data wrappers: Object, Array, Function, Boolean, Number, String
// Utility objects: Math, Date, RegExp
// Error objects: Error
// Object
// o.constrcutor
// o.toString()
// o.valueOf()
// Array objects have a length while ordinary objects do not
(function() {
title_line('array has length');
var o1 = [];
var o2 = {};
console.log(typeof o1, o1.length);
console.log(typeof o2, o2.length); // os.length is undefined
})();
// change the size of an array via setting its size
(function() {
title_line('change array size');
var o = [1,2,3,4,5];
console.log(o);
o.length = 10;
console.log(o);
console.log('o[7] = ', o[7]); // undefined
})();
// other array methods
(function() {
title_line('more array operations');
var o = [1,2,3,4,5,6,7,8,9];
console.log(o.join('-o-')); // elements of o is automatically converted to string
// the two arguments of slice specify the start and end point (not included)
console.log(o.slice(1,2)); // [1, 2)
// the second argument of splice specifies the number of elements to remove
var oo = o.splice(2,3, 'deux', 'trois');
console.log('oo=', oo, 'o=', o);
})();
// the constructor of a function
(function() {
title_line('the constructor of a function');
var sum = Function('a', 'b', 'return a + b;');
console.log(sum(1,4));
})();