pythia

Pythia was the name of the high priestess of the Temple of Apollo at Delphi. She specifically served as its oracle and was known as the Oracle of Delphi.

Deterministically mock values from Math.random.

Values can be given as a single number, an array or a function returning a value. Optionally stop mocking after the values have been used.

Values are verified to be of type number and in the interval [0,1[, as this is what Math.random returns. An error is thrown when unexpected values are detected.

Installation

$ npm install --save-dev the-pythia

Usage

const pythia = require("the-pythia");

pythia.predict(0.5);

console.log(Math.random()); // 0.5

API

predict(prediction [, options])

Parameters

prediction

The value(s) to return.

Accepts the following types:

| Type | Math.random() returns | | ---------- | ----------------------- | | number | the given number | | array | each number in the array per subsequent call | | function | the return value of the function, until it returns something falsy |

options

An options object that only has one settings: repeat. Setting this to false will reset Math.random when the value(s) have been exhausted. Has no effect on function predictions, since it resets as soon as the function returns something falsy.

isPredicting()

Returns a boolean reflecting if pythia is predicting random values.

forget()

Reset Math.random to its original functionality.

reset()

Alias for forget().

Examples

const pythia = require("the-pythia");

// Type: number
pythia.predict(0.1982);

Math.random(); // 0.1982
Math.random(); // 0.1982


// Type: number, no repeat
pythia.predict(0.42, { repeat: false });

Math.random(); // 0.42
Math.random(); // Psuedo-random value between 0 and 1


// Type: array
pythia.predict([0.31, 0.41, 0.52]);

Math.random(); // 0.31
Math.random(); // 0.41
Math.random(); // 0.52
Math.random(); // 0.31


// Type: array, no repeat
pythia.predict([0.31, 0.41, 0.52], { repeat: false });

Math.random(); // 0.31
Math.random(); // 0.41
Math.random(); // 0.52
Math.random(); // Psuedo-random value between 0 and 1


// Type: function
let fakeRandomCalls = 0;
pythia.predict(() => {
  if (fakeRandomCalls++ > 2) return false;
  return 0.8219
});

Math.random(); // 0.8219
Math.random(); // 0.8219
Math.random(); // 0.8219
Math.random(); // Psuedo-random value between 0 and 1


// Unexpected predictions
pythia.predict(12); // Throws PythiaError: "Random value must be greater than or equal to zero"
pythia.predict(-1); // Throws PythiaError: "Random value must be less than one"