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"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.



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}.

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