How to: String Formatting

The guide shows how to create an expression that will return a formatted string. Before starting, create a local Modbus device, a tag with the name source_tag and the data format FLOAT (32-bit floating point).

DISCLAIMER

You can just use the format function from MosText. This guide is given for an example of working with scripts and modules

Open Monokot Server Administrator, double-click Scripts on the Server Explorer pane and go to the Modules tab. Click the New Module button and name the module Sprintf. Insert the following code into the code editor:

// Return a formatted string 
function sprintf() {     
    var regex = /%%|%(\d+\$)?([-+\'#0 ]*)(\*\d+\$|\*|\d+)?(\.(\*\d+\$|\*|\d+))?([scboxXuidfegEG])/g;
    var a = arguments, i = 0, format = a[i++];

    // pad()
    var pad = function (str, len, chr, leftJustify) {
        if (!chr) { chr = ' '; }
        var padding = (str.length >= len) ? '' : Array(1 + len - str.length >>> 0).join(chr);
        return leftJustify ? str + padding : padding + str;
    };

    // justify()
    var justify = function (value, prefix, leftJustify, minWidth, zeroPad, customPadChar) {
        var diff = minWidth - value.length;
        if (diff > 0) {
            if (leftJustify || !zeroPad) {
                value = pad(value, minWidth, customPadChar, leftJustify);
            } else {
                value = value.slice(0, prefix.length) + pad('', diff, '0', true) + value.slice(prefix.length);
            }
        }
        return value;
    };

    // formatBaseX()
    var formatBaseX = function (value, base, prefix, leftJustify, minWidth, precision, zeroPad) {
        // Note: casts negative numbers to positive ones
        var number = value >>> 0;
        prefix = prefix && number && { '2': '0b', '8': '0', '16': '0x'}[base] || '';
        value = prefix + pad(number.toString(base), precision || 0, '0', false);
        return justify(value, prefix, leftJustify, minWidth, zeroPad);
    };

    // formatString()
    var formatString = function (value, leftJustify, minWidth, precision, zeroPad, customPadChar) {
        if (precision != null) {
            value = value.slice(0, precision);
        }
        return justify(value, '', leftJustify, minWidth, zeroPad, customPadChar);
    };

    // doFormat()
    var doFormat = function (substring, valueIndex, flags, minWidth, _, precision, type) {
        var number;
        var prefix;
        var method;
        var textTransform;
        var value;

        if (substring == '%%') { return '%'; }

        // parse flags
        var leftJustify = false, positivePrefix = '', zeroPad = false, prefixBaseX = false, customPadChar = ' ';
        var flagsl = flags.length;
        for (var j = 0; flags && j < flagsl; j++) {
            switch (flags.charAt(j)) {
                case ' ': positivePrefix = ' '; break;
                case '+': positivePrefix = '+'; break;
                case '-': leftJustify = true; break;
                case "'": customPadChar = flags.charAt(j + 1); break;
                case '0': zeroPad = true; break;
                case '#': prefixBaseX = true; break;
            }
        }

        // parameters may be null, undefined, empty-string or real valued
        // we want to ignore null, undefined and empty-string values
        if (!minWidth) {
            minWidth = 0;
        } else if (minWidth == '*') {
            minWidth = +a[i++];
        } else if (minWidth.charAt(0) == '*') {
            minWidth = +a[minWidth.slice(1, -1)];
        } else {
            minWidth = +minWidth;
        }

        // Note: undocumented perl feature:
        if (minWidth < 0) {
            minWidth = -minWidth;
            leftJustify = true;
        }

        if (!isFinite(minWidth)) {
            throw new Error('sprintf: (minimum-)width must be finite');
        }

        if (!precision) {
            precision = 'fFeE'.indexOf(type) > -1 ? 6 : (type == 'd') ? 0 : undefined;
        } else if (precision == '*') {
            precision = +a[i++];
        } else if (precision.charAt(0) == '*') {
            precision = +a[precision.slice(1, -1)];
        } else {
            precision = +precision;
        }

        // grab value using valueIndex if required?
        value = valueIndex ? a[valueIndex.slice(0, -1)] : a[i++];

        switch (type) {
            case 's': return formatString(String(value), leftJustify, minWidth, precision, zeroPad, customPadChar);
            case 'c': return formatString(String.fromCharCode(+value), leftJustify, minWidth, precision, zeroPad);
            case 'b': return formatBaseX(value, 2, prefixBaseX, leftJustify, minWidth, precision, zeroPad);
            case 'o': return formatBaseX(value, 8, prefixBaseX, leftJustify, minWidth, precision, zeroPad);
            case 'x': return formatBaseX(value, 16, prefixBaseX, leftJustify, minWidth, precision, zeroPad);
            case 'X': return formatBaseX(value, 16, prefixBaseX, leftJustify, minWidth, precision, zeroPad).toUpperCase();
            case 'u': return formatBaseX(value, 10, prefixBaseX, leftJustify, minWidth, precision, zeroPad);
            case 'i':
            case 'd':
                number = parseInt(+value, 10);
                prefix = number < 0 ? '-' : positivePrefix;
                value = prefix + pad(String(Math.abs(number)), precision, '0', false);
                return justify(value, prefix, leftJustify, minWidth, zeroPad);
            case 'e':
            case 'E':
            case 'f':
            case 'F':
            case 'g':
            case 'G':
                number = +value;
                prefix = number < 0 ? '-' : positivePrefix;
                method = ['toExponential', 'toFixed', 'toPrecision']['efg'.indexOf(type.toLowerCase())];
                textTransform = ['toString', 'toUpperCase']['eEfFgG'.indexOf(type) % 2];
                value = prefix + Math.abs(number)[method](precision);
                return justify(value, prefix, leftJustify, minWidth, zeroPad)[textTransform]();
            default: return substring;
        }
    };

    return format.replace(regex, doFormat);
}

Press Ctrl + Enter to apply the change in the code editor.

By default, the ECMAScript 5 standard does not provide a string formatting function, but since there are a huge number of developers who code in JavaScript, most typical tasks have already been solved, as in this case. The sprintf function (https://github.com/alexei/sprintf.js) has existed for several years now and is analogous to the PHP sprintf function.

Go to the Expressions tab and click the New Expression button. For the expression that appeared, set the name Message and specify the data type STRING. Insert the following code into the expression code editor:

var val = context.data['source_tag_trig'].state.value;
return sprintf('Formatted number: %.3f', val);

Press Ctrl + Enter to apply the change in the code editor. Go to the Triggers tab and click Add Data.... Select the previously created tag (source_tag) as the data source for the trigger. Enter source_tag_trig as the name (key) of the trigger.

Go to the Imports tab and click the checkbox of the Sprintf module.

In order for the changes to take effect on the server, click the Sync button. If you switch to Go Online mode, you will see a picture similar to the following (in my case, the number 0.123456 is displayed).