用<select value =“ myFunction”>之类的方法在JS中“动态”调用函数

如何解决用<select value =“ myFunction”>之类的方法在JS中“动态”调用函数

我正在尝试学习如何动态创建对象以及使用JS和HTML将函数应用到它们。如何使用<select>下拉菜单的文本/值尽可能直接在对象上调用函数？过去，我曾在数组中使用过函数，if语句或条件链，但这似乎是多余的工作。

我也愿意就动态对象实例创建提出建议，因为我不确定本示例中的方法是否是最佳实践。

这是我的例子：

HTML

<!DOCTYPE html>
<html>
    <head>
    </head>
    <body>
        <input id="name" placeholder="name">
        <button id="new">add new object</button>
        <br>
        <input id="property" placeholder="property value">
        <select id="functions">
            <option>apply a function</option>
            <option value="myFunction()">sum</option>
            <option value="myFunction2()">multiply</option>
        </select>
    </body>
    <script src="dynamic-objects.js"></script>
</html>

// Class and its functions
function myClass() {
    this.existingProperty = 5 
}
myClass.prototype.myFunction = function () {
    this.resultProperty = this.newProperty + this.existingProperty
}
myClass.prototype.myFunction2 = function () {
    this.resultProperty = this.newProperty * this.existingProperty
}

// Memory
const locoparentis = []
let nameField = ''
let propField = 0

// Name of object instance of myClass (for example: type dogs into the brower/HTML "name" input)
document.querySelector('#name').addEventListener('change',(e)=>{
    nameField = e.target.value
})
// Add the new objeect instance to the array (for example: click add new object to create an object called dogs with an existingProperty of 5)
document.querySelector('#new').addEventListener('click',()=>{
    locoparentis[nameField] = new myClass()
    console.log(locoparentis)
})
// Create/set new property in object instance (for example: typing 9 in the property value input sets dogs' newProperty to 9)
document.querySelector('#property').addEventListener('input',(e)=>{
    locoparentis[nameField].newProperty = Number(e.target.value)
    console.log(locoparentis)
})

// Apply prototypical functions on object instance (for example: chosing sum outputs 14 into the console.)
document.querySelector('#functions').addEventListener('change',(e)=>{
    console.log(e.target.value)
    //HOW CAN I CHANGE THIS INTO SOMETHING LIKE locoparentis[nameField].e.target.value() 
    e.target.value === "myFunction()" ? locoparentis[nameField].myFunction() : locoparentis[nameField].myFunction2()
    console.log(locoparentis[nameField].resultProperty)
})

说明：我可以通过在名称myClass中键入名称来动态创建<input>的新对象实例，但是我想对<select>和原型使用类似的方法myClass的功能。

解决方法

// Class and its functions
function myClass() {
    this.existingProperty = 5;
}
myClass.prototype.myFunction = function () {
    this.resultProperty = this.newProperty + this.existingProperty;
}
myClass.prototype.myFunction2 = function () {
    this.resultProperty = this.newProperty * this.existingProperty;
}

// Memory
const locoParentis = {};
let nameField;

// Name of object instance of myClass (for example: type dogs into the brower/HTML "name" input)
document.querySelector('#name').addEventListener('change',(e)=>{
    nameField = e.target.value;
})
// Add the new objeect instance to the array (for example: click add new object to create an object called dogs with an existingProperty of 5)
document.querySelector('#new').addEventListener('click',()=>{
    locoParentis[nameField] = new myClass();
    console.log(locoParentis);
})
// Create/set new property in object instance (for example: typing 9 in the property value input sets dogs' newProperty to 9)
document.querySelector('#property').addEventListener('input',(e)=>{
    locoParentis[nameField].newProperty = Number(e.target.value);
    console.log(locoParentis);
})

document.querySelector('#functions').addEventListener('change',(e)=>{
    // you can check here for undefined 
    locoParentis[nameField][e.target.value]();
    console.log(locoParentis[nameField].resultProperty);
})

<!DOCTYPE html>
<html>
    <head>
    </head>
    <body>
        <input id="name" placeholder="name">
        <button id="new">add new object</button>
        <br>
        <input id="property" placeholder="property value">
        <select id="functions">
            <option>apply a function</option>
            <option value="myFunction">sum</option>
            <option value="myFunction2">multiply</option>
        </select>
    </body>
</html>

尝试这个。

但是要考虑一些事情。您无需添加单独的“添加新对象”按钮。当您选择相加或相乘时，可以创建一个新实例。