javascript

//world hello
var str = 'hello world';
var pattern = /([a-z]+)\s([a-z]+)/;
var n_str = str.replace(pattern, "$2 $1");

typeof "John"                 // Returns "string"
typeof 3.14                   // Returns "number"
typeof NaN                    // Returns "number"
typeof false                  // Returns "boolean"
typeof [1,2,3,4]              // Returns "object"
typeof {name:'John', age:34}  // Returns "object"
typeof new Date()             // Returns "object"
typeof function () {}         // Returns "function"
typeof myCar                  // Returns "undefined" *
typeof null                   // Returns "object"

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi");   // Adds "Kiwi" to fruits

//foreach
const a = ["a", "b", "c"];
a.forEach((element) => {
    console.log(element);
});

//for
for (let i = 0; i < 5; i++) {
  text += "The number is " + i + "<br>";
}

//格式化时间数据
formatDate: function (date) {
    var d = new Date(date),
    month = "" + (d.getMonth() + 1),
    day = "" + d.getDate(),
    year = d.getFullYear();
    if (month.length < 2) month = "0" + month;
    if (day.length < 2) day = "0" + day;
    return [year, month, day].join("-");
},

//获取前7天Date数据
const now = new Date();
const today = new Date(now.getFullYear(), now.getMonth(), now.getDate());
const minDate = new Date(today);
minDate.setDate(minDate.getDate() - 7);
const maxDate = new Date(today);

# slice()
const str = 'Coding Beauty';
const firstTwoChars = str.slice(0, 2);
console.log(firstTwoChars); // Co

# substring()
const str = 'Coding Beauty';
const firstTwoChars = str.substring(0, 2);
console.log(firstTwoChars); // Co