1. 多久以前

js 计算几天前，几小时前，几分钟前

/**
 * @param {date} time 订单时间（日期格式或者时间戳）
 * @param {number} num 返回几个时间单位，如：1周(num=1)，1周2天(num=2),1周2天1小时(num=3)
 */
function timeFormat(time, num = 1) {
  let timeArr = [
    365 * 24 * 60 * 60 * 1000,
    30 * 24 * 60 * 60 * 1000,
    7 * 24 * 60 * 60 * 1000,
    24 * 60 * 60 * 1000,
    60 * 60 * 1000,
    60 * 1000,
    1000,
  ];
  let unit = ["年", "个月", "周", "天", "小时", "分钟", "秒钟"];
  let timeDiff = Date.now() - new Date(time).getTime();
  if (timeDiff <= 0) return "刚刚";
  let tip = [];
  for (let i = 0; i < timeArr.length; i++) {
    if (timeDiff < timeArr[i]) continue;

    let temp = Math.floor(timeDiff / timeArr[i]);
    timeDiff = timeDiff % timeArr[i];

    if (temp > 0) {
      tip.push(temp + unit[i]);
    }

    if (tip.length >= num) break;
  }
  return tip.join("") + "前";
}
console.log(timeFormat("2023-5-10 17:42:09", 1));
// 1小时前

2. 判断两个对象的值是否一致

/**
 * @description 判断两个对象的值是否一致
 * @param {Object} b
 * @param {Object} a
 */
function isObjectValueEqual(a, b) {
  if (a === b) return true;
  let aProps = Object.getOwnPropertyNames(a);
  let bProps = Object.getOwnPropertyNames(b);
  if (aProps.length !== bProps.length) return false;
  for (let prop in a) {
    if (b.hasOwnProperty(prop)) {
      if (typeof a[prop] === "object") {
        if (!isObjectValueEqual(a[prop], b[prop])) return false;
      } else if (a[prop] !== b[prop]) {
        return false;
      }
    } else {
      return false;
    }
  }
  return true;
}

let a = { a: 1, b: 2 };
let b = { b: 2, a: 1 };
console.log(isObjectValueEqual(a, b)); // true

3. JavaScript 小数精度计算

/**
 * 数字运算（主要用于小数点精度问题）
 * [see](https://juejin.im/post/6844904066418491406#heading-12)
 * @param {number} a 前面的值
 * @param {"+"|"-"|"*"|"/"} type 计算方式
 * @param {number} b 后面的值
 * @example
 * ```js
 * // 可链式调用
 * const res = computeNumber(1.3, "-", 1.2).next("+", 1.5).next("*", 2.3).next("/", 0.2).result;
 * console.log(res);
 * ```
 */
function computeNumber(a, type, b) {
  /**
   * 获取数字小数点的长度
   * @param {number} n 数字
   */
  function getDecimalLength(n) {
    const decimal = n.toString().split(".")[1];
    return decimal ? decimal.length : 0;
  }
  /**
   * 修正小数点
   * @description 防止出现 `33.33333*100000 = 3333332.9999999995` && `33.33*10 = 333.29999999999995` 这类情况做的处理
   * @param {number} n
   */
  const amend = (n, precision = 15) =>
    parseFloat(Number(n).toPrecision(precision));
  const power = Math.pow(
    10,
    Math.max(getDecimalLength(a), getDecimalLength(b))
  );
  let result = 0;

  a = amend(a * power);
  b = amend(b * power);

  switch (type) {
    case "+":
      result = (a + b) / power;
      break;
    case "-":
      result = (a - b) / power;
      break;
    case "*":
      result = (a * b) / (power * power);
      break;
    case "/":
      result = a / b;
      break;
  }

  result = amend(result);

  return {
    /** 计算结果 */
    result,
    /**
     * 继续计算
     * @param {"+"|"-"|"*"|"/"} nextType 继续计算方式
     * @param {number} nextValue 继续计算的值
     */
    next(nextType, nextValue) {
      return computeNumber(result, nextType, nextValue);
    },
  };
}

4.复制功能

/**
 * 复制文本
 * @param {string} text 复制的内容
 * @param {() => void} success 成功回调
 * @param {(error: string) => void} fail 出错回调
 */
function copyText(text, success = null, fail = null) {
  text = text.replace(/(^\s*)|(\s*$)/g, "");
  if (!text) {
    typeof fail === "function" && fail("复制的内容不能为空！");
    return;
  }
  const id = "the-clipboard";
  /**
   * 粘贴板节点
   * @type {HTMLTextAreaElement}
   */
  let clipboard = document.getElementById(id);
  if (!clipboard) {
    clipboard = document.createElement("textarea");
    clipboard.id = id;
    clipboard.readOnly = true;
    clipboard.style.cssText =
      "font-size: 15px; position: fixed; top: -1000%; left: -1000%;";
    document.body.appendChild(clipboard);
  }
  clipboard.value = text;
  clipboard.select();
  clipboard.setSelectionRange(0, text.length);
  const state = document.execCommand("copy");
  // clipboard.blur(); // 设置readOnly就不需要这行了
  if (state) {
    typeof success === "function" && success();
  } else {
    typeof fail === "function" && fail("复制失败");
  }
}

5.格式化时间

/**
 * 格式化日期
 *
 * @param {(Object|string|number)} time
 * @param {string} format 
 * @returns {string | null}
 */
function parseTime(time, format = '{y}-{m}-{d} {h}:{i}:{s}') {
  if (!time) return "";
  if (arguments.length === 0) {
    return null;
  }
  let date;
  if (typeof time === "object") {
    date = time;
  } else {
    if (typeof time === "string") {
      if (/^[0-9]+$/.test(time)) {
        time = parseInt(time);
      } else {
        time = time.replace(new RegExp(/-/gm), "/");
      }
    }

    if (typeof time === "number" && time.toString().length === 10) {
      time = time * 1000;
    }
    date = new Date(time);
  }
  const formatObj = {
    y: date.getFullYear(),
    m: date.getMonth() + 1,
    d: date.getDate(),
    h: date.getHours(),
    i: date.getMinutes(),
    s: date.getSeconds(),
    a: date.getDay(),
  };
  const time_str = format.replace(/{([ymdhisa])+}/g, (result, key) => {
    const value = formatObj[key];
    if (key === "a") {
      return ["日", "一", "二", "三", "四", "五", "六"][value];
    }
    return value.toString().padStart(2, "0");
  });
  return time_str;
}

参考

前端常用功能 js-掘金 (opens new window)