常用的JS方法

常用的JS方法

1、base64转二进制(Blob)数据

方法一

function b64toBlob(b64Data, contentType = '', sliceSize = 512) {
  const byteCharacters = atob(b64Data);
  const byteArrays = [];

  for (let offset = 0; offset < byteCharacters.length; offset += sliceSize) {
    const slice = byteCharacters.slice(offset, offset + sliceSize);

    const byteNumbers = new Array(slice.length);
    for (let i = 0; i < slice.length; i++) {
      byteNumbers[i] = slice.charCodeAt(i);
    }

    const byteArray = new Uint8Array(byteNumbers);

    byteArrays.push(byteArray);
  }

  const blob = new Blob(byteArrays, { type: contentType });
  return blob;
}

方法二

function base64toBlob(b64Data, contentType = '') {
  const byteCharacters = atob(b64Data);
  const byteNumbers = new Array(byteCharacters.length);
  for (let i = 0; i < byteCharacters.length; i++) {
    byteNumbers[i] = byteCharacters.charCodeAt(i);
  }
  const byteArray = new Uint8Array(byteNumbers);

  const blob = new Blob([byteArray], { type: contentType });
  return blob;
}

---

2、格式化参数对象

function jsonForm(obj) {
  let result = '';
  Object.keys(obj).forEach((key, index) => {
    result += `${index === 0 ? '' : '&'}${key}=${encodeURIComponent(obj[key])}`;
  });
  return result;
}

---

3、判断值是否在区间内

function valueBettween({
  min = required('最小值min'),
  max = required('最大值max'),
  value = required('输入值value'),
}) {
  return Math.min(Math.max(min, value), max);
}

4、格式化Date

① 格式时间

• 如为今天，则格式为：上/下午 时：分；
• 如为昨天，则格式为：昨天 时：分；
• 其余时间格式为：年-月-日 时：分。

formatDateForMsg(date) {
  const curDate = new Date();
  // + 1000 处理零点零零问题
  const oneDayS = 86400000;
  const resH = Help.formatD(date.getHours());
  const resM = Help.formatD(date.getMinutes());
  const resHM = `${resH}:${resM}`;
  const DayS = date.getTime() + 1000;
  const todayS = ((curDate.getHours() * 60 + curDate.getMinutes()) * 60 + curDate.getSeconds()) * 1000;
  const lastDayS = curDate.getTime() - todayS;
  const differS = DayS - lastDayS;
  if (differS >= 0) {
    if (resH < 12) {
      return `上午  ${resHM}`;
    }
    return `下午  ${resHM}`;
  }
  if (differS + oneDayS < 0) {
    const y = date.getFullYear();
    const m = Help.formatD(date.getMonth() + 1);
    const d = Help.formatD(date.getDate());
    return `${y}-${m}-${d} ${resHM}`;
  }
  return `昨天  ${resHM}`;
}

② 格式化小于10的数字——‘09’

formatD(num) {
    if (num < 0) {
      return num;
    }
    return num < 10 ? `0${num}` : num;
  }