简介
使用 Node.js 的前置学习系列笔记之一
前置条件
- Node.js 已安装 【安装笔记】
样例需求
- NA
学习笔记
注释
单行注释 // line comment 和 块注释 /* block comment */，在注释中的代码和文字不会被读取执行。
样例代码 0000_js_comment.js
// this is the first line comment
// console.log('Line comment to ignore this code!');
console.log('Hello World!');
/*
Multi-line comment
console.log('Block comment, not execute this code!');
*/
执行结果
(base) myserver@myserver:/pega/nodejs/get_start/pre_0001_js_grammar$ node 0000_js_comment.js
Hello World!
标识符
// 变量
const a = 1;
var b = 2;
// 方法
function fn(msg) {
console.log(msg);
}
// 对象
const obj = {
key: 'value'
};
// 类
class SampleClass {
#private_property = 'private value' // 私有变量
public_property = 'public value'
}
lbl: console.log('label'); // 标签
模板文字（模板字符串）
模板文字是用反引号 (```) 字符分隔的文字，允许使用嵌入表达式的 多行字符串、字符串插值 以及称为 标记模板 的特殊构造。
样例代码 0002_js_template_literals.js
// 模板字符串中使用转义字符
console.log(`\`` === "`"); //true
// 多行字符串
const multi_line = `Line 1
Line 2
Line 3` // 第三行前面有4个空格
console.log(multi_line);
// 字符串插值
const val_1 = 5;
const val_2 = 10;
console.log("Fifteen is " + (val_1 + val_2) + " and\nnot " + (2 * val_1 + val_2) + ".");
console.log(`Fifteen is ${val_1 + val_2} and
not ${2 * val_1 + val_2}.`);
// 标记模板
const person = "Apple"
const age = "28"
function myTagFn(myString, personExpresion, ageExpression) {
const str0 = myString[0]; // 第一个 expression 以前的字符串
const str1 = myString[1]; // 第一个 expression 至第二个 expression 中间的字符串
const str2 = myString[2]; // 第二个 expression 之后的字符串
const mapToAgeStr = ageExpression < 100 ? "youngster" : "centenarian";
// 拼接转化后字符串
return `${str0}${personExpresion}${str1}${mapToAgeStr}${str2}`;
}
const outputStr = myTagFn`That ${person} is a ${age}.`;
console.log(outputStr);
运行结果
(base) myserver@myserver:/pega/nodejs/get_start/pre_0001_js_grammar$ node 0002_js_template_literals.js
true
Line 1
Line 2
Line 3
Fifteen is 15 and
not 20.
Fifteen is 15 and
not 20.
That Apple is a youngster.
通用模板生成器样例代码 0003_js_common_template.js
// define common template
function common_template (myStrings, ...keys) {
return (...values) => {
// Get object to dict
const dict = values[values.length - 1] || {};
// add first string to result
const result = [myStrings[0]];
// use forEach to get value
keys.forEach((key, i) => {
const value = Number.isInteger(key) ? values[key] : dict[key];
result.push(value, myStrings[i+1]);
});
// join result with "" and return
return result.join("");
}
}
// example 1 without object
const my_temp_1 = common_template`${0}${1}${0}!`;
const my_temp_2 = common_template(["","","","!"],0,1,0);
console.log(`my_temp_1: ${my_temp_1('Y',"A")}`);
console.log(`my_temp_2: ${my_temp_2('Y',"A")}`);
// example 2 with object
const my_temp_3 = common_template`${0} ${"foo"}!`;
const my_temp_4 = common_template([""," ","!"],0,"foo");
console.log(`my_temp_3: ${my_temp_3("hello",{foo: "world"})}`);
console.log(`my_temp_4: ${my_temp_4("hello",{foo: "world"})}`);
// example 3 with complex string and object
const my_temp_5 = common_template`I'm ${"name"}, I'm almost ${"age"} years old. I like play ${0}.`;
const my_temp_6 = common_template(["I'm ",", I'm almost "," years old. I like play ","."],"name","age",0);
console.log(`my_temp_5: ${my_temp_5("basketball",{name: "Apple",age: 28})}`);
console.log(`my_temp_6: ${my_temp_6("basketball",{name: "Apple",age: 28})}`);
运行结果
(base) myserver@myserver:/pega/nodejs/get_start/pre_0001_js_grammar$ node 0003_js_common_template.js
my_temp_1: YAY!
my_temp_2: YAY!
my_temp_3: hello world!
my_temp_4: hello world!
my_temp_5: I'm Apple, I'm almost 28 years old. I like play basketball.
my_temp_6: I'm Apple, I'm almost 28 years old. I like play basketball.
更多内容请查看文中参考链接，谢谢！