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Classes-Constructor.js
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170 lines (136 loc) · 2.88 KB
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//: 9.1 => Always use class. Avoid manipulating prototype directly.
/* Why? Class syntax is more concise and easier to reason about. */
// bad
function Queue(contents = []) {
this.queue = [...contents];
}
Queue.prototype.pop = function () {
const value = this.queue[0];
this.queue.splice(0, 1);
return value;
};
// class
class Queue {
constructor(contents = []) {
this.queue = [...contents];
}
pop() {
const value = this.queue[0];
this.queue.splice(0, 1);
return value;
}
}
//: 9.2 => Use extends for inheritance
/* Why? It is a built-in way to inherit prototype functionality without breaking instancof. */
// bad
const inherits = require("inherits");
function PeekableQueue(contents) {
Queue.apply(this, contents);
}
inherits(PeekableQueue, Queue);
PeekableQueue.prototype.peek = function () {
return this.queue[0];
};
// good
class PeekableQueue extends Queue {
peek() {
return this.queue[0];
}
}
//: 9.3 => Methods can return this to help with method chaining.
// bad
Jedi.prototype.jump = function () {
this.jumping = true;
return true;
};
Jedi.prototype.setHeight = function (height) {
this.height = height;
};
const luke = new Jedi();
luke.jump(); // => true
luke.setHeight(20); // => undefined
// good
class Jedi {
jump() {
this.jumping = true;
return this;
}
setHeight(height) {
this.height = height;
return this;
}
}
const luke2 = new Jedi();
luke.jump().setHeight(20);
//: 9.4 => /* It's okay to write a custom toString() method, just make sure it works successfully and causes no side effects. */
class Jedi {
constructor(options = {}) {
this.name = options.name || "no name";
}
getName() {
return this.name;
}
toString() {
return `Jedi - ${this.getName()}`;
}
}
//: 9.5 => /* Classes have a default constructor if one is not specified. An empty constructor function or one that just delegates to a parent class is unnecessary. eslint: no-useless-constructor */
// bad
class Jedi {
constructor() {}
getName() {
return this.name;
}
}
// bad
class Rey extends Jedi {
constructor(...args) {
super(...args);
}
}
// good
class Rey extends Jedi {
constructor(...args) {
super(...args);
this.name = 'Rey';
}
}
//: Avoid duplicate class members. eslint: no-dupe-class-members
/* Why? Duplicate class member declarations will silently prefer the last one - having duplicates is almost certainly a bug. */
// bad
class Foo {
bar() { return 1; }
bar() { return 2; }
}
// good
class Foo {
bar() { return 1; }
}
// good
class Foo {
bar() { return 2; }
}
// bad
class Foo {
bar() {
console.log('bar');
}
}
// good - this is used
class Foo {
bar() {
console.log(this.bar);
}
}
// good - constructor is exempt
class Foo {
constructor() {
// ...
}
}
// good - static methods aren't expected to use this
class Foo {
static bar() {
console.log('bar');
}
}