kerryChen95

      .item { 
        margin-bottom: 20px;
        padding: 10px; 
        font-size: 0;
        border: 1px solid #efefef;
      }
      .item .pic , 
      .item .content {
        display: table-cell;
        *display: inline;

kerryChen95

Real undefined valued element

Way 1: in operator, and for...in loop

Due to indexes are not even defined for empty element, in operator return false.

var arr = new Array(5);
console.log(1 in arr); // false

arr[1] = undefined;

kerryChen95

var foo = 'foo';
console.log(this.foo); // 'foo'

In global execution context, declaring a variable means add a property to this

(function () {
  var bar = 'bar';
 console.log(this.bar); // undefined

kerryChen95

var objInGlobal = {
  a: 'a',
  b: 'b'
};

(function (baseTypeVar, referTypeVar, notPassedArg) {
  baseTypeVar = 2;
  console.log(baseTypeVar === arguments[0]); // true
 

kerryChen95

Array in JavaScript is actually object:

• automatically maintains indexed values and length property.
• its constructor is Array which provides some methods to be inherited, e.g. forEach.
• may use non-sequence memory since it's an object.

Array in C is different, it always uses sequence memory, at this point, it is real array.

So what it means?

kerryChen95

// example 1
(function () {
  console.log(typeof func); // 'function'
  function func () {}
  console.log(typeof func); // 'function'
})();


// example 2
(function () {

kerryChen95

example 1

var sum = 0.1 + 0.2; // 0.30000000000000004

// way 1:
Number(sum.toFixed(5)) === 0.3; // true

// way 2:
(sum - 0.3) < 1e-5; // true

kerryChen95

var i, arr = ["dwdwad","dwdawd","dwdwad","ddd","sss"], target = 'ddd';

var hash = {};

for(i = 0; i < arr.length; ++i) {
  hash[arr[i]] = i;
}
console.log(hash[target]);

kerryChen95

// Why?
// too long? How long is too long?

Math.ceil(3.0000000000000001); // 3

Math.ceil(3.000000000000001);  // 4

kerryChen95

REST: Representational state transfer 表征状态转移

表示各个HTTP请求之间是无状态的，也就是说单个HTTP请求包含了所作操作需要的所有信息。请求会使资源的状态发生变化（GET除外，但如果产生访问记录也算状态变化的话，那么GET也算）。