问如何在JavaScript中用循环将十六进制转换为十进制

EN

function hexToDec(hex) {
    var result = 0, digitValue;
    hex = hex.toLowerCase();
    for (var i = 0; i < hex.length; i++) {
        digitValue = '0123456789abcdef'.indexOf(hex[i]);
        result = result * 16 + digitValue;
    }
    return result;
}

console.log(hexToDec('FE'));

function hexToDec(hex) {
    return hex.toLowerCase().split('').reduce( (result, ch) =>
        result * 16 + '0123456789abcdefgh'.indexOf(ch), 0);
}

console.log(hexToDec('FE'));

// The purpose of the function is to convert Hex to Decimal.  
// This is done by adding each of the converted values.
function hextoDec(val) {
  
    // Reversed the order because the added values need to 16^i for each value since 'F' is position 1 and 'E' is position 0
    var hex = val.split('').reverse().join('');
  
    // Set the Decimal variable as a integer
    var dec = 0;
  
    // Loop through the length of the hex to iterate through each character
    for (i = 0; i < hex.length; i++) {
      
        // Obtain the numeric value of the character A=10 B=11 and so on..
        // you could also change this to var conv = parseInt(hex[i], 16) instead
        var conv = '0123456789ABCDEF'.indexOf(hex[i]);
      
        // Calculation performed is the converted value * (16^i) based on the position of the character
        // This is then added to the original dec variable.  'FE' for example
        // in Reverse order [E] = (14 * (16 ^ 0)) + [F] = (15 * (16 ^ 1)) 
        dec += conv * Math.pow(16, i);
      
    }
  
    // Returns the added decimal value
    return dec;
}

console.log(hextoDec('FE'));

function doit(hex) {
    var num = 0;
    for(var x=0;x<hex.length;x++) {
        var hexdigit = parseInt(hex[x],16);
        num = (num << 4) | hexdigit;
    }
    return num;
}