备忘单是我们开发人员始终需要的参考。因此,这里我编译了许多JavaScript参考代码。查看分类并找到它。这篇文章对学习者和开发人员都有帮助。
JavaScript Number方法备忘单
- toExponential():以字符串形式返回表示Number对象的字符串
function expo(x, f) {
return
Number.parseFloat(x).toExponential(f);
}
console.log(expo(123456, 2));
// -> 1.23e+5
- toFixed():使用定点表示法格式化数字
function financial(x) {
return Number.parseFloat(x).toFixed(2);
}
console.log(financial(123.456));
// -> 123.46
- toPrecision():以指定的精度返回表示Number对象的字符串
function precise(x) {
return
Number.parseFloat(x).toPrecision(4);
}
console.log(precise(123.456));
// -> 123.5
- toString():返回表示指定Number对象的字符串
function hexColour(c) {
if (c < 256) {
return Math.abs(c).toString(16);
}
return 0;
}
console.log(hexColour(233));
// -> e9
- valueOf():返回数字对象的包装原始值
const numObj = new Number(42);
console.log(typeof numObj);
// -> object
const num = numObj.valueOf();
console.log(num);
// -> 42
console.log(typeof num);
// -> number
JavaScript循环备忘单
- 对于循环
for (var i = 0; < 10; i++) {
console.log(i + ": " + i * 3 + "<br />");
}
// -> 0: 0<br />
// -> 1: 3<br />
// -> ...
let a = [1, 2, 3];
var sum = 0;
for (var i - 0; i <a.length; i++) {
sum += a[i];
} // pasing an array
console.log(sum);
// -> 6
- While循环
var i = 1; // initialize
while (i < 100) { // enters the cycle if statement is true
i *= 2; // increment to avoid infinte loop
console.log(i + ", "); // output
}
// 2,
// 4,
// ...
// 128,
- 循环执行
var i = 1; // initialize
while (i < 100) { // enters the cycle asleast once
i *= 2; // increment to avoid infinte loop
console.log(i + ", "); // output
} while (1 < 100); // repeats cycle if statement is true at the end
// 2,
// 4,
// ...
// 128,
- 打破
for (var i = 0; i < 10; i++) {
if (i == 5 ) { break; } // stops and exits the cycle
console.log(i + ", "); // Lat output number is 4
}
// -> 0,
// -> 1,
// ...
// -> 4,
- 继续
for (var i = 0; i < 10; i++) {
if (i == 5 ) { continue; } // skips the rest of the cycle
console.log(i + ", "); // skips 5
}
// -> 0,
// -> 1,
// ...
// -> 9,
JavaScript字符串方法备忘单
- charAt():返回指定索引处的字符
const sentence = "Jeff bezos is now the second richest.";
const index = 4;
console.log(`The character at index ${index} is ${sentence.charAt(index)}`);
// The character at index 4 is f
- concat():连接两个或多个字符串,并返回所连接字符串的副本
const str1 = "Hello";
cosnt str2 = "World";
console.log(str1.concat(" ", str2));
// -> Hello World
console.log(str2.concat(", ", str1));
// -> World, Hello
- replace():搜索子字符串(或正则表达式)和字符串之间的匹配项,并将匹配的子字符串替换为新的子字符串
const p = "Talk is cheap. Show me the work. - Someone";
console.log(p.replace("work", "code"));
// -> Talk is cheap. Show me the code. - Someone
- search():搜索正则表达式和字符串之间的匹配项,并返回匹配项的位置
const paragraph = "The quick brown fox jumps over the lazy dog.";
// any character that is not a word character or whitespace
const regex = /[^ws]/g;
console.log(paragraph.search(regex));
// -> 43
- slice():提取字符串的一部分并返回新的字符串
const str = "The quick brown fox jumps over the lazy dog.";
consolelog(str.slice(31));
// -> the lazy dog
console.log(str.slice(4, 19));
// -> quick brown fox
- trim():删除字符串两端的空格
const greeting = " Hello world! ";
console.log(greeting);
// -> Hello world!
console.log(greeting.trim());
// -> Hello world!
- substr():从字符串中提取字符,从指定的起始位置开始,直到指定的字符数
const str = "Mozilla";
console.log(str.substr(1, 2));
// -> oz
console.log(stre.substr(2));
// -> zilla
- toLowerCase():将字符串转换为小写字母
const sentence = "Elon became the richest last night.";
console.log(sentence.toLowerCase());
// -> elon became the richest last night.
JavaScript数组方法指导表
- concat():连接两个或多个数组,并返回联接数组的副本
let array1 = ["a", "b", "c"];
let array2 = ["d", "e", "f"];
let array3 = array1.concat(array2);
console.log(array3);
// -> Array(6) ["a", "b", "c", "d", "e", "f" ]
- indexOf():在数组中搜索元素并返回其位置
let beasts = ["ant", "bison", "camel", "duck", "bison"];
console.log(beasts.indexOf("bison"));
// -> 1
// start from index 2
console.log(beasts.indexOf("bison", 2));
// -> 4
- join():将数组的所有元素连接到一个字符串中
let elements = ["Fire", "Air", "Water"];
console.log(elements.join());
// -> Fire,Air,Water
console.log(elements.join(" "));
// -> Fire Air Water
- pop():删除数组的最后一个元素,并返回该元素
let plants = ["broccoli", "cauliflower", "cabbage", "kale", "tomato"];
console.log(plants.pop());
// -> tomato
console.log(plants);
// -> Array(4) ["brocxoli", "cauliflower", "cabbage", "kale"]
- reverse():反转数组中元素的顺序
let array1 = ["one", "two", "three"];
console.log("array1:", array1);
// -> array1: Array(3) [ "one", "two", "three" ]
let reversed = array1.reverse();
console.log("reversed", reversed);
// -> reversed: Array(3) [ "three", "two", "one" ]
- shift():删除数组的第一个元素,并返回该元素
let array1 = [1, 2, 3];
let firstElement = array1.shift();
console.log(array1);
// -> Array [ 2, 3 ]
- sort():对数组的元素进行排序
let months = ["March", "Jan", "Feb", "Dec"];
months.sort();
console.log(months);
// -> Array(4) [ "Dec", "Feb", "Jan", "March" ]
- toString():将数组转换为字符串,并返回结果
const array1 = [1, 2, "a", "1a"];
console.log(array1.toString());
// -> 1,2,a,1a
JavaScript数据类型备忘单
var age = 18; // Number
var name = "Rahul"; // string
var name = {first:"Rahul", last:"Singh"}; // object
var truth = false; // boolean
var sheets = ["HTML", "CSS", "JS"]; // array
var a; typeof a; // undefined
var a = null; // value null
JavaScript运算符备忘单
a = b + c - d; // addition, substraction
a = b * (c / d); // multiplication, division
x = 100 % 48; // modulo. 100 / 48 remainder = 4
a++; b--; // postfix increment and decrement
变量备忘单
- var:最常见的变量。可以重新分配,但只能在函数中访问。执行代码时,用var定义的变量移到顶部。
- const:在出现在代码中之前无法重新分配并且无法访问
- let:与const类似,但是可以重新分配let变量,但不能重新声明
var a; // variable
var b = "init"; // string
var c = "Hi" + "" + "Rahul"; // "Hi Rahul"
var d = 1 + 2 + "3"; // "33"
var e = [2,3,5,8]; // array
var f = false; // boolean
var g = /()/; // RegEx
var h = function(){}; // function object
const PI = 3.14; // constant
var a = 1, b = 2, c = a + b; // one line
let z = 'zzz'; // block scope local variable
获取日期方法提示表
- getFullYear():根据当地时间返回指定日期的年份
const moonLanding = new Date("January 08, 69 00:20:10");
console.log(moonLanding.getFullYear());
// -> 1969
- getMonth():根据本地时间返回指定日期中的月份,该值从零开始(其中零表示一年的第一个月)。
const moonLanding = new Date("January 08, 69 00:20:10");
console.log(moonLanding.getMonth()); // (January gives 0)
// -> 6
- getDate():根据当地时间返回指定日期的月份
const birthday = new Date("June 16, 2004 23:14:00");
const date1 = birthday.getDate();
console.log(date1);
// -> 19
- getHours():根据当地时间返回指定日期的小时
const birthday = new Date("June 16, 04 4:20");
console.log(birthday.getHours());
// -> 4
- getMinutes():根据当地时间返回指定日期的分钟
const birthday = new Date("June 16, 04 04:10");
console.log(birthday.getMinutes());
// -> 20
- getSeconds()根据当地时间返回指定日期中的秒数
const moonLanding = newDate("June 16, 69 00:23:11");
console.log(moonLanding.getSeconds());
// -> 18
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