对象的自定义检查函数

【Custom inspection functions on objects】

对象也可以定义它们自己的 [util.inspect.custom](depth, opts, inspect) 函数，util.inspect() 在检查对象时会调用该函数并使用其返回结果。

【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.】

import { inspect } from 'node:util';

class Box {
  constructor(value) {
    this.value = value;
  }

  [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);

console.log(inspect(box));
// "Box< true >"const { inspect } = require('node:util');

class Box {
  constructor(value) {
    this.value = value;
  }

  [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);

console.log(inspect(box));
// "Box< true >"拷贝

自定义 [util.inspect.custom](depth, opts, inspect) 函数通常返回一个字符串，但也可以返回任何类型的值，util.inspect() 会相应地格式化该值。

【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().】

import { inspect } from 'node:util';

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

console.log(inspect(obj));
// "{ bar: 'baz' }"const { inspect } = require('node:util');

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

console.log(inspect(obj));
// "{ bar: 'baz' }"拷贝