如何修复一个简单的 js 计算器（返回未定义）

Question

我的任务是仅使用一个 JS 对象创建一个计算器。无论我做什么，它都会返回“未定义”，我无法理解出了什么问题。我知道它与默认值有关，但不故意声明“未定义”也会返回错误。所有的方法都应该可以正常工作，但不知何故他们就是不行。

var Calculator = {
  x: undefined,
  y: undefined,
  addition: function() {
    var result = this.x + this.y;
    return result;
  },
  division: function() {
    var result = this.x / this.y;
    return result;
  },
  multiplication: function() {
    var result = this.x * this.y;
    return result;
  },
  subtraction: function() {
    var result = this.x - this.y;
    return result;
  },
  calulation: function() {
    var mathSign;
    this.x = +prompt('Please insert a first number: ');
    this.y = +prompt('Please enter a second number: ');
    if (isNaN(this.x) || isNaN(this.y)) {
      alert('Please insert a number!');
      this.x = +prompt('Please insert a first number: ');
      this.y = +prompt('Please enter a second number: ');
    }
    mathSign = prompt('Please enter a math symbol: (+, -, *, /)');
    if (mathSign == '+' || mathSign == '-' || mathSign == '*' || mathSign == '/') {
      switch (mathSign) {
        case '+':
          this.addition();
        case '-':
          this.subtraction();
        case '*':
          this.multiplication();
        case '/':
          this.division();
      }
    } else {
      alert('An input should be a math symbol! (+, -, *, /)')
    }
  }
}

console.log(Calculator.calulation());

Answer 1

你永远不会从calculation()函数中返回任何值。您需要在您的内部返回函数结果的值switch()：

switch(mathSign) {
    case '+': 
        return this.addition();
    case '-':
        return this.subtraction();
    case '*': 
        return this.multiplication();
    case '/':
        return this.division();
}