ES6解构对象赋值函数参数默认值 [英] ES6 destructuring object assignment function parameter default value

问题描述

我正在这里介绍对象解构在传递函数参数时使用的示例 对象解构演示

Hi I was going through examples of object destructuring use in passing function parameters here Object Destructuring Demo

function drawES6Chart({size = 'big', cords = { x: 0, y: 0 }, radius = 25} = **{}**) {
  console.log(size, cords, radius);
 // do some chart drawing
}

 // In Firefox, default values for destructuring assignments are not yet  
 implemented (as described below). 
 // The workaround is to write the parameters in the following way:
   // ({size: size = 'big', cords: cords = { x: 0, y: 0 }, radius: radius =  
      25} = **{}**)

 drawES6Chart({
    cords: { x: 18, y: 30 },
    radius: 30
});

谁能告诉我在上面用粗体(嵌入双星)标记的函数参数末尾使用空对象赋值的原因是什么?

Can anybody let me know what is reason of using empty object assignment at the end of function parameter which I have marked in bold(embedded in double stars) above?

推荐答案

如果你使用它，并且调用不带参数的函数，它的工作原理是:

If you use it, and call the function with no parameters, it works:

function drawES6Chart({size = 'big', cords = { x: 0, y: 0 }, radius = 25} = {}) {
  console.log(size, cords, radius);
 // do some chart drawing
}

drawES6Chart();

如果不是，则抛出错误:

if not, an error is thrown:

类型错误:无法将未定义转换为对象

TypeError: can't convert undefined to object

function drawES6Chart({size = 'big', cords = { x: 0, y: 0 }, radius = 25}) {
  console.log(size, cords, radius);
 // do some chart drawing
}

drawES6Chart();

这篇关于ES6解构对象赋值函数参数默认值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！