"Limiting the Range of a Number": Chapbook (v1.0.0)


This example demonstrates how to limit a numeric variable to a value between a set range. This process is commonly known as clamping.

The example adds a clamp() function to the existing built-in Math global JavaScript object, which can then be called to achieve the desired result.

This added function is then used within the Vars Section to set a value before using an expression to show its value within the passage itself.

Live Example

Download: Live Example

Twee Code

:: StoryTitle
Chapbook: Limiting Range of Number

:: UserScript[script]
(function () {

    Object.defineProperty(Number.prototype, 'clamp', {
        configurable : true,
        writable     : true,

        value(/* min, max */) {
            if (this == null) { // lazy equality for null
                throw new TypeError('Number.prototype.clamp called on null or undefined');

            if (arguments.length !== 2) {
                throw new Error('Number.prototype.clamp called with an incorrect number of parameters');

            var min = Number(arguments[0]);
            var max = Number(arguments[1]);

            if (min > max) {
                var tmp = min;
                min = max;
                max = tmp;

            return Math.min(Math.max(this, min), max);

        Returns the given numerical clamped to the specified bounds.

            → Limit numeric variable to a value between 1 and 10 inclusive.
            example: Math.clamp(variable, 1, 10)

            → Limit result of mathematical operation to a value between 1 and 10 inclusive.
            variable: Math.clamp(variable + 5, 1, 10)
    Object.defineProperty(Math, 'clamp', {
        configurable : true,
        writable     : true,

        value(num, min, max) {
            var value = Number(num);
            return Number.isNaN(value) ? NaN : value.clamp(min, max);


:: Start
exampleNumber: 11
exampleResult: Math.clamp(exampleNumber, 1, 10)

Despite *exampleNumber* being {exampleNumber}, it will be "clamped" to the highest number given to the function (10). The result is {exampleResult}.

Download: Twee Code

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