对象的自定义检查函数

\Custom inspection functions on objects

对象也可以定义自己的 [util.inspect.custom](depth, opts, inspect) 函数,util.inspect() 将在检查对象时调用并使用其结果。

\Objects may also define their own [util.inspect.custom](depth, opts, inspect) function, which util.inspect() will invoke and use the result of when inspecting the object.

const util = require('node:util');
class Box {
 constructor(value) {
 this.value = value;
 }
 [util.inspect.custom](depth, options, inspect) {
 if (depth < 0) {
 return options.stylize('[Box]', 'special');
 }
 const newOptions = Object.assign({}, options, {
 depth: options.depth === null ? null : options.depth - 1
 });
 // Five space padding because that's the size of "Box< ".
 const padding = ' '.repeat(5);
 const inner = inspect(this.value, newOptions)
 .replace(/\n/g, `\n${padding}`);
 return `${options.stylize('Box', 'special')}< ${inner} >`;
 }
}
const box = new Box(true);
util.inspect(box);
// Returns: "Box< true >" 拷贝

自定义的 [util.inspect.custom](depth, opts, inspect) 函数通常返回一个字符串,但也可能返回一个由 util.inspect() 相应格式化的任何类型的值。

\Custom [util.inspect.custom](depth, opts, inspect) functions typically return a string but may return a value of any type that will be formatted accordingly by util.inspect().

const util = require('node:util');
const obj = { foo: 'this will not show up in the inspect() output' };
obj[util.inspect.custom] = (depth) => {
 return { bar: 'baz' };
};
util.inspect(obj);
// Returns: "{ bar: 'baz' }" 拷贝