《深入理解JavaScript特性》学习总结1-ES6基础知识点总结 （下）

function cast() {
        return [...arguments]
      }
      cast("a", "b", "c");
      //["a", "b", "c"]

[..."show me"]
      // ["s", "h", "o", "w", " ", "m", "e"]

function cast() {
        return ["left", ...arguments, "right"];
      }
      cast("left", "a", "b", "c", "right");
      //["left","a", "b", "c", "right"]

const all = [1, ...[2, 3, 4, 5, 6], 7, ...[8, 9]];
      console.log(all);
      // [1, 2, 3, 4, 5, 6, 7, 8, 9]

const text = `algorithm`;

 const text = `1+1=2`;
 console.log(text);
 // 1+1=2

const num=2
const text = `1+1=${num}`;
console.log(text);
// 1+1=2
const text = `1+1=${1+1}`;
console.log(text);
// 1+1=2

// 原方法
      const escaped = 
      "The first line\n\
      A second line\n\
      Then a third line";
      const concatenated =
      "The first line\n" `
      "A second line\n" `
      "Then a third line";
      const joined = ["The first line", "A second line", "Then a third line"];
      // ES6模板字符串
      const multiline = 
      `The first line
      A second line 
      Then a third line`;

function getParagraph(){
    return `
      Dear Rod
      this is a template literal string...
      Nico
`
}
getParagraph()
//"
//      Dear Rod
//      
//      this asfsdfasfasdfsdfs
//      asfasdfasdf
//   
//      Nico
//"

const text = String.raw`"\n" is taken literally.
      It'll be escaped instead of interpreted`;
      console.log(text);
      // "\n" is taken literally.
      // It'll be escaped instead of interpreted

function study() {
   console.log(a)
   var a = 1;
}
study()//undefined

function study(item) {
   if (item == 1) {
      var a = true;
   }
   return a
}
study(1); //true

let algorithm = {};
      {
        let language = {};
        {
          let questions = {};
        }
        // 在此尝试访问questions会报异常
      }
      // 在此尝试访问language会报异常
      // 在此尝试访问questions会报异常

for (var i = 0; i < 5; i++) {
  setTimeout(() => console.log(i));
}
// 5
// 5
// 5
// 5
// 5
for (let i = 0; i < 5; i++) {
  setTimeout(() => console.log(i));
}
// 0
// 1
// 2
// 3
// 4

console.log(study);//ReferenceError: study is not defined
 let study = "algorithm";

// const 遵循块级作用域规则
      const study = algorithm;
      {
        const study = language;
        console.log(study); //language
      }
      console.log(study); //algorithm

const algorithm = "nignt";
 const language;//语法错误，缺少初始化

const algorithm = "nignt";
 const language = 1;
if (algorithm === "nignt") {
        language = 2;//捕获类型错误：分配给常量变量
 }