JavaScript 核心基础：变量提升、数据类型与对象字面量详解

/* 函数声明 */
foo(); // "bar"  
function foo() {
 console.log("bar");
}  

/* 函数表达式  表达式定义的函数，成为匿名函数。匿名函数没有函数提升。*/  
baz(); // TypeError: baz is not a function
//此时的"baz"相当于一个声明的变量，类型为undefined。
由于baz只是相当于一个变量，因此浏览器认为"baz()"不是一个函数。
var baz = function() {
 console.log("bar2");
};

const MY_OBJECT = {"key": "value"};
MY_OBJECT.key = "otherValue";

x = "The answer is " + 42 // "The answer is 42"
y = 42 + " is the answer" // "42 is the answer"

"37" - 7 // 30
"37" + 7 // "377"

"1.1" + "1.1" = "1.11.1"
(+"1.1") + (+"1.1") = 2.2  // 注：加入括号为清楚起见，不是必需的。

var unusualPropertyNames = {
 "": "An empty string",
 "!": "Bang!"
}
console.log(unusualPropertyNames."");  // 语法错误: Unexpected string
console.log(unusualPropertyNames[""]); // An empty string
console.log(unusualPropertyNames.!);  // 语法错误: Unexpected token !
console.log(unusualPropertyNames["!"]); // Bang!

var foo = {a: "alpha", 2: "two"};
console.log(foo.a);  // alpha
console.log(foo[2]);  // two
//console.log(foo.2); // Error: missing ) after argument list
//console.log(foo[a]); // Error: a is not defined
console.log(foo["a"]); // alpha
console.log(foo["2"]); // two

var obj = {
  // __proto__
  __proto__: theProtoObj,
  // Shorthand for ‘handler: handler'
  handler,
  // Methods
  toString() {
   // Super calls
   return "d " + super.toString();
  },
  // Computed (dynamic) property names
  [ 'prop_' + (() => 42)() ]: 42
};

// 引号转义
var quote = "He read /"The Cremation of Sam McGee/" by R.W. Service.";
// 转义反斜线
var home = "c://temp";
// 转义换行 一条语句拆成多行书写
var str = "this string /
is broken /
across multiple/
lines."
console.log(str);  // this string is broken across multiplelines.
// Javascript没有“heredoc”语法，但可以用行末的换行符转义和转义的换行来近似实现 
var poem = 
"Roses are red,/n/
Violets are blue./n/
I'm schizophrenic,/n/
And so am I."