js 各种进制转换，转ascll码等

因为近期做小程序，蓝牙连接硬件，需要根据module bus通信协议解析数据，用到了很多标题的算法转换，借此总结一下。

十六进制转十进制

function hex_dec(hex) {
    var len = hex.length,
        a = new Array(len),
        code;
    for (var i = 0; i < len; i++) {
        code = hex.charCodeAt(i);
        if (48 <= code && code < 58) {
            code -= 48;
        } else {
            code = (code & 0xdf) - 65 + 10;
        }
        a[i] = code;
    }
    return a.reduce(function (acc, c) {
        acc = 16 * acc + c;
        return acc;
    }, 0);
} 

十进制转十六进制

function dec_hex(val){
return ("0" + (Number(val).toString(16))).slice(-2).toUpperCase()
}

十六进制转二进制（需要借用到hex_dec，也就是需要先转换成十进制再转成二进制）

function hex_bin(hex, len) {
    var res = hex_dec(hex).toString(2);
    return (Array(len).join(0) + res).slice(-len);
}

二进制转十六进制（网上的一种办法）

function bin_hex(str) {
    let hex_array = [{ key: 0, val: "0000" }, { key: 1, val: "0001" }, { key: 2, val: "0010" }, { key: 3, val: "0011" }, { key: 4, val: "0100" }, { key: 5, val: "0101" }, { key: 6, val: "0110" }, { key: 7, val: "0111" },
    { key: 8, val: "1000" }, { key: 9, val: "1001" }, { key: 'a', val: "1010" }, { key: 'b', val: "1011" }, { key: 'c', val: "1100" }, { key: 'd', val: "1101" }, { key: 'e', val: "1110" }, { key: 'f', val: "1111" }]
    let value = ''
    let list = []
    if (str.length % 4 !== 0) {
      let a = "0000"
      let b = a.substring(0, 4 - str.length % 4)
      str = b.concat(str)
    }
    while (str.length > 4) {
      list.push(str.substring(0, 4))
      str = str.substring(4);
    }
    list.push(str)
    for (let i = 0; i < list.length; i++) {
      for (let j = 0; j < hex_array.length; j++) {
        if (list[i] == hex_array[j].val) {
          value = value.concat(hex_array[j].key)
          break
        }
      }
    }
    return value
  }

十六进制转ArrayBuffer

function hex_buf(hexStr) {
    var count = hexStr.length / 2;
    let buffer = new ArrayBuffer(count);
    let dataView = new DataView(buffer);
    for (var i = 0; i < count; i++) {
        var curCharCode = parseInt(hexStr.substr(i * 2, 2), 16);
        dataView.setUint8(i, curCharCode);
    }
    return buffer;
}

ArrayBufer转十六进制

function buf_hex(buffer) { // buffer is an ArrayBuffer
    return Array.prototype.map.call(new Uint8Array(buffer), x => ('00' + x.toString(16)).slice(-2)).join('');
}

十六进制转ASCII码

function hex_ascll(hexCharCodeStr) {
  var trimedStr = hexCharCodeStr.trim();
  var rawStr = trimedStr.substr(0, 2).toLowerCase() === "0x" ? trimedStr.substr(2) : trimedStr;
  var len = rawStr.length;
  if (len % 2 !== 0) {
    alert("存在非法字符!");
    return "";
  }
  var curCharCode;
  var resultStr = [];
  for (var i = 0; i < len; i = i + 2) {
    curCharCode = parseInt(rawStr.substr(i, 2), 16);
    resultStr.push(String.fromCharCode(curCharCode));
  }
  return resultStr.join("");
}