I learned JavaScript Basics in Udacity. This is the link: JavaScript Basics.
What I’ve learned
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console.log();//Let interpreter(Chrome dev tools) print out the content. 让解释器打印出括号里面的内容。 -
var variableName = 'variableValue'; // define a variable and put a value to it. We can also just declare a variable without giving a value to it. 定义一个变量，并指定该变量的值。当然也可以只声明该变量不赋值。 -
[string].replace([old], [new]); // return the changed value. See MDN link: [String.prototype.replace()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace)返回修改后的数值。最好定义一个变量接收该值。 -
str.slice(beginSlice[, endSlice]); // extracts a section of a string and returns a new string. see MDN link: [String.prototype.slice()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice) 取出字符串里的一部分，并返回这个取出来的字符串。中括号内可选，如果没输入中括号内的值，则一直取到字符串末尾。不能用在数组里。 -
str.toUpperCase(); // returns the calling string value converted to uppercase. See MDN link: [String.prototype.toUpperCase()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase) 返回该字符串的大写值。str.toLowerCase()返回小写。同理。 -
Array: a group of objects. The items can be string, number, array, or function.
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str.length; // return the length of the string or array. 后面没有括号。 -
arr.pop(); // removes the **last** element from an array and returns that element. See link: [Array.prototype.pop()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/pop) 剔除数组的最后一个元素并将该元素返回。括号中不能加参数。 -
arr.push(); // adds one or more elements to the end of an array and returns the new length of the array. See link: [Array.prototype.push()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push) 把括号里面的元素加到数组最后，并返回该数组的长度。 -
str.split([separator[, limit]]); // splits a [String](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String) object into an array of strings by separating the string into substrings. See link: [String.prototype.split()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split) 把一个字符串按指定的分隔符分隔成一个数组。中括号里面的limit是可选内容。如果不写，则将整个字符串按分隔符操作一遍；如果写3，则仅返回前3个元素。 -
str.trim(); //removes whitespace from both ends of a string. Whitespace in this context is all the whitespace characters (space, tab, no-break space, etc.) and all the line terminator characters (LF, CR, etc.). See link: [String.prototype.trim()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trim) 去掉字符串最前和最后的空格。常和str.split()一起用，以此防止生成的数组中，数组头和数组尾含有空元素。举例说明：var str = " Today is Tuesday! ";var strArr1 = str.split(" ");console.log(strArr1); // ["", "Today", "is", "Tuesday!", ""]var strArr2 = str.trim().split(" ");console.log(strArr2); // ["Today", "is", "Tuesday!"] -
str = arr.join([separator = ',']); // joins all elements of an array into a string. See link: [Array.prototype.join()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join)把数组中所有元素合并成一个字符串，并返回该字符串。方括号中是可选。如果加了内容，则每两个数组之间会加此内容。通常会加逗号或者空格。 -
var objName = {"name": "shisaq","age": 32}; // This is an object. A object is capable to contain string, number, and array. It's like an array. But actually, array is a special object. Because an array just has a list from 0 to the length, but an object can define every value's name. 数组是一种特殊的对象。数组只是一个有序列表，而对象可以给任何值定义任何名字。 -
JSON: JavaScript Object Notation. JavaScript对象标识法。跟上面举出的例子一样，JavaScript对象怎么写，JSON就怎么写。主要用来存取数据。注意最后一行末尾不要加逗号（,）。
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if Statements.
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=== is safer than ==
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for in loops: Use
forEachorforto iterate over arrays like:
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<code>countries = ['Argentina', 'China', 'England'];</code>
Use for-in to loop over objects like
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<code>countries = {'country1':'Argentina', 'country2':'China','country3':'England'};</code>
being careful to wrap the content of the for-in in a conditional statement that tests if the key is part of the object:
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<code>myObj = {'country1':'Germany', 'country2':'Argentina'};
for (key in myObj){
if (myObj.hasOwnProperty(key)) {
console.log(myObj[key]);
}
}</code>
For more information, please refer to the loop section of the Udacity Front End Style Guide.
