Add Comparator.

Author: trekhleb

src/utils/comparator/Comparator.js

@@ -0,0 +1,46 @@
+export default class Comparator {
+  /**
+   * @param {function(a: *, b: *)} [compareFunction]
+   */
+  constructor(compareFunction) {
+    this.compare = compareFunction || Comparator.defaultCompareFunction;
+  }
+
+  /**
+   * @param {(string|number)} a
+   * @param {(string|number)} b
+   * @returns {number}
+   */
+  static defaultCompareFunction(a, b) {
+    if (a === b) {
+      return 0;
+    }
+
+    return a < b ? -1 : 1;
+  }
+
+  equal(a, b) {
+    return this.compare(a, b) === 0;
+  }
+
+  lessThen(a, b) {
+    return this.compare(a, b) < 0;
+  }
+
+  greaterThen(a, b) {
+    return this.compare(a, b) > 0;
+  }
+
+  lessThenOrEqual(a, b) {
+    return this.lessThen(a, b) || this.equal(a, b);
+  }
+
+  greaterThenOrEqual(a, b) {
+    return this.greaterThen(a, b) || this.equal(a, b);
+  }
+
+  reverse() {
+    const compareOriginal = this.compare;
+    this.compare = (a, b) => compareOriginal(b, a);
+  }
+}

src/utils/comparator/__test__/Comparator.test.js

@@ -0,0 +1,50 @@
+import Comparator from '../Comparator';
+
+describe('Comparator', () => {
+  it('should compare with default comparator function', () => {
+    const comparator = new Comparator();
+
+    expect(comparator.equal(0, 0)).toBeTruthy();
+    expect(comparator.equal(0, 1)).toBeFalsy();
+    expect(comparator.equal('a', 'a')).toBeTruthy();
+    expect(comparator.lessThen(1, 2)).toBeTruthy();
+    expect(comparator.lessThen(-1, 2)).toBeTruthy();
+    expect(comparator.lessThen('a', 'b')).toBeTruthy();
+    expect(comparator.lessThen('a', 'ab')).toBeTruthy();
+    expect(comparator.lessThen(10, 2)).toBeFalsy();
+    expect(comparator.lessThenOrEqual(10, 2)).toBeFalsy();
+    expect(comparator.lessThenOrEqual(1, 1)).toBeTruthy();
+    expect(comparator.lessThenOrEqual(0, 0)).toBeTruthy();
+    expect(comparator.greaterThen(0, 0)).toBeFalsy();
+    expect(comparator.greaterThen(10, 0)).toBeTruthy();
+    expect(comparator.greaterThenOrEqual(10, 0)).toBeTruthy();
+    expect(comparator.greaterThenOrEqual(10, 10)).toBeTruthy();
+    expect(comparator.greaterThenOrEqual(0, 10)).toBeFalsy();
+  });
+
+  it('should compare with custom comparator function', () => {
+    const comparator = new Comparator((a, b) => {
+      if (a.length === b.length) {
+        return 0;
+      }
+
+      return a.length < b.length ? -1 : 1;
+    });
+
+    expect(comparator.equal('a', 'b')).toBeTruthy();
+    expect(comparator.equal('a', '')).toBeFalsy();
+    expect(comparator.lessThen('b', 'aa')).toBeTruthy();
+    expect(comparator.greaterThenOrEqual('a', 'aa')).toBeFalsy();
+    expect(comparator.greaterThenOrEqual('aa', 'a')).toBeTruthy();
+    expect(comparator.greaterThenOrEqual('a', 'a')).toBeTruthy();
+
+    comparator.reverse();
+
+    expect(comparator.equal('a', 'b')).toBeTruthy();
+    expect(comparator.equal('a', '')).toBeFalsy();
+    expect(comparator.lessThen('b', 'aa')).toBeFalsy();
+    expect(comparator.greaterThenOrEqual('a', 'aa')).toBeTruthy();
+    expect(comparator.greaterThenOrEqual('aa', 'a')).toBeFalsy();
+    expect(comparator.greaterThenOrEqual('a', 'a')).toBeTruthy();
+  });
+});