It sounds like you want the object parameter to be optional, and also each of the properties in the object to be optional. In the example, as provided, overload syntax isn't needed. I wanted to point out some bad practices in some of the answers here. Granted, it's not the smallest possible expression of essentially writing box = { x: 0, y: 87, width: 4, height: 0 }, but this provides all the code hinting niceties you could possibly want from the class as described. This example allows you to call a function with one, some, all, or none of the parameters and still get default values.
/** @class */
class Box {
public x?: number;
public y?: number;
public height?: number;
public width?: number;
constructor(params: Box = {} as Box) {
// Define the properties of the incoming `params` object here.
// Setting a default value with the `= 0` syntax is optional for each parameter
let {
x = 0,
y = 0,
height = 1,
width = 1
} = params;
// If needed, make the parameters publicly accessible
// on the class ex.: 'this.var = var'.
/** Use jsdoc comments here for inline ide auto-documentation */
this.x = x;
this.y = y;
this.height = height;
this.width = width;
}
}
Need to add methods? A verbose but more extendable alternative:
The Box class above can work double-duty as the interface since they are identical. If you choose to modify the above class, you will need to define and reference a new interface for the incoming parameters object since the Box class no longer would look exactly like the incoming parameters. Notice where the question marks (?:) denoting optional properties move in this case. Since we're setting default values within the class, they are guaranteed to be present, yet they are optional within the incoming parameters object:
interface BoxParams {
x?: number;
// Add Parameters ...
}
class Box {
public x: number;
// Copy Parameters ...
constructor(params: BoxParams = {} as BoxParams) {
let { x = 0 } = params;
this.x = x;
}
doSomething = () => {
return this.x + this.x;
}
}
无论你选择哪种方式来定义你的类，这种技术都提供了类型安全的护栏，同时还可以灵活地编写以下任何一种:
const box1 = new Box();
const box2 = new Box({});
const box3 = new Box({x:0});
const box4 = new Box({x:0, height:10});
const box5 = new Box({x:0, y:87,width:4,height:0});
// Correctly reports error in TypeScript, and in js, box6.z is undefined
const box6 = new Box({z:0});
编译后，您将看到如何仅在可选值未定义时使用默认设置;它避免了广泛使用(但容易出错)的回退语法var = isOptional || default的陷阱;通过检查void 0，它是undefined的缩写:
编译后的输出
var Box = (function () {
function Box(params) {
if (params === void 0) { params = {}; }
var _a = params.x, x = _a === void 0 ? 0 : _a, _b = params.y, y = _b === void 0 ? 0 : _b, _c = params.height, height = _c === void 0 ? 1 : _c, _d = params.width, width = _d === void 0 ? 1 : _d;
this.x = x;
this.y = y;
this.height = height;
this.width = width;
}
return Box;
}());
附录:设置默认值:错误的方式
|| (or)操作符
在设置默认回退值时，如其他一些答案所示，请考虑||/或操作符的危险。下面的代码说明了设置默认值的错误方法。当你对0，"，null, undefined, false, NaN等假值进行计算时，你可能会得到意想不到的结果:
var myDesiredValue = 0;
var result = myDesiredValue || 2;
// This test will correctly report a problem with this setup.
console.assert(myDesiredValue === result && result === 0, 'Result should equal myDesiredValue. ' + myDesiredValue + ' does not equal ' + result);
Object.assign (params)
在我的测试中，使用es6/typescript解构object可以比object .assign快15-90%。使用解构形参只允许您分配给对象的方法和属性。例如，考虑这个方法:
class BoxTest {
public x?: number = 1;
constructor(params: BoxTest = {} as BoxTest) {
Object.assign(this, params);
}
}
如果另一个用户没有使用TypeScript，并试图放置一个不属于TypeScript的参数，比如，他们可能会尝试放置一个z属性
var box = new BoxTest({x: 0, y: 87, width: 4, height: 0, z: 7});
// This test will correctly report an error with this setup. `z` was defined even though `z` is not an allowed property of params.
console.assert(typeof box.z === 'undefined')
