Merge pull request #66 from variadicjs/range

add range

Author: tdnelson2

README.md

@@ -102,7 +102,7 @@ Computability:
 - [X] Factoral
 - [X] Minimum
 - [X] Maximum
-- [ ] Range
+- [X] Range
 - [X] Average
 - [X] Mode
 - [X] Median

index.js

@@ -22,6 +22,7 @@ module.exports = Object.assign(
   require('./lib/median.js'),
   require('./lib/minimum.js'),
   require('./lib/mode.js'),
+  require('./lib/range.js'),
   require('./lib/populationStandardDeviation.js'),
   require('./lib/populationVariance.js'),
   require('./lib/sampleStandardDeviation.js'),

lib/range.js

@@ -0,0 +1,41 @@
+// JS can only safely represent and compare integers
+// between Number.MAX_SAFE_INTEGER and Number.MAX_SAFE_INTEGER
+const testMaxMinSafe = (params) => {
+  if (params.some(param => param > Number.MAX_SAFE_INTEGER || param < Number.MIN_SAFE_INTEGER)) {
+    throw new Error('Cannot reliably find the range of numbers larger than 9,007,199,254,740,991 or smaller than -9,007,199,254,740,991');
+  }
+};
+
+const handleErrors = (params) => {
+  if (params.length === 0) throw new Error('Must provide one or more paramters');
+  if (params.some(param => typeof param !== 'number')) {
+    throw new Error('One of your parameters does not evaluate to a number');
+  }
+  testMaxMinSafe(params);
+};
+
+/**
+ * This function returns the difference between the largest and smallest values
+ * @memberof variadic
+ * @author tdnelson2
+ * @param {...*} params - One or more parameters.
+ */
+exports.range = (...params) => {
+  handleErrors(params);
+
+  // Exit early if there is only one value
+  if (params.length === 1) return 0;
+
+  // Assign first value in the param list to the `high` and `low` variables
+  let [high, low] = [params[0], params[0]];
+  const [, ...nums] = params;
+
+  // Loop through the rest of the parameters and compare/update `high` and `low`
+  for (const num of nums) {
+    if (num > high) { high = num; } else if (num < low) { low = num; }
+  }
+
+  const result = high - low;
+  testMaxMinSafe([result]);
+  return result;
+};

spec/rangeSpec.js

@@ -0,0 +1,47 @@
+const { range } = require('../lib/range');
+
+describe('range', () => {
+  it('should return either 0 or a positive number', () => {
+    const result = range(-296.028, 296.028, 42, +'-42');
+    expect(result >= 0).toBe(true);
+  });
+
+  it('should return the difference between the largest and smallest values', () => {
+    const result = range(1.6, -2.3325, 596960, 3938475.31589, +'-395757.326518');
+    expect(result).toEqual(4334232.642408);
+  });
+
+  it('should return 0 when all there numbers are identical', () => {
+    const result = range(296.028, 296.028, 296.028, 296.028);
+    expect(result).toEqual(0);
+  });
+
+  it('should return 0 when only one number is provided', () => {
+    const result = range(296.028);
+    expect(result).toEqual(0);
+  });
+
+  it('should throw an error when no parameters are provided', () => {
+    expect(range).toThrow();
+  });
+
+  it('should throw an error when at least one parameter does not evaluate to a number', () => {
+    expect(() => range(42, 'foo', 'bar')).toThrow();
+  });
+
+  it('should throw an error when at least one parameter evaluates to a number larger than Number.MAX_SAFE_INTEGER', () => {
+    expect(() => range(Number.MAX_SAFE_INTEGER + 1)).toThrow();
+  });
+
+  it('should throw an error when at least one parameter evaluates to a number smaller than Number.MIN_SAFE_INTEGER', () => {
+    expect(() => range(Number.MIN_SAFE_INTEGER - 1)).toThrow();
+  });
+
+  it('should throw an error when result is number larger than Number.MAX_SAFE_INTEGER', () => {
+    expect(() => range(1.6, -2.3325, 9007199254740990, 596960, -3938475)).toThrow();
+  });
+
+  it('should throw an error when result is number smaller than Number.MIN_SAFE_INTEGER', () => {
+    expect(() => range(1.6, -2.3325, -9007199254740990, 596960, 3938475)).toThrow();
+  });
+});