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1-js/04-object-basics/06-constructor-new/4-calculator-extendable/_js.view/solution.js

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+function Calculator() {
+
+  var methods = {
+    "-": function(a, b) {
+      return a - b;
+    },
+    "+": function(a, b) {
+      return a + b;
+    }
+  };
+
+  this.calculate = function(str) {
+
+    var split = str.split(' '),
+      a = +split[0],
+      op = split[1],
+      b = +split[2]
+
+    if (!methods[op] || isNaN(a) || isNaN(b)) {
+      return NaN;
+    }
+
+    return methods[op](a, b);
+  }
+
+  this.addMethod = function(name, func) {
+    methods[name] = func;
+  };
+}

1-js/04-object-basics/06-constructor-new/4-calculator-extendable/_js.view/test.js

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+var calculator;
+before(function() {
+  calculator = new Calculator;
+});
+
+it("calculate(12 + 34) = 46", function() {
+  assert.equal(calculator.calculate("12 + 34"), 46);
+});
+
+it("calculate(34 - 12) = 22", function() {
+  assert.equal(calculator.calculate("34 - 12"), 22);
+});
+
+it("добавили умножение: calculate(2 * 3) = 6", function() {
+  calculator.addMethod("*", function(a, b) {
+    return a * b;
+  });
+  assert.equal(calculator.calculate("2 * 3"), 6);
+});
+
+it("добавили возведение в степень: calculate(2 ** 3) = 8", function() {
+  calculator.addMethod("**", function(a, b) {
+    return Math.pow(a, b);
+  });
+  assert.equal(calculator.calculate("2 ** 3"), 8);
+});