未捕获的类型错误:无法读取 null index.html:24 的属性“已检查" [英] Uncaught TypeError: Cannot read property 'checked' of null index.html:24

问题描述

我是 JavaScript 新手，希望你能帮助我，如主题，null 属性.

I'm newbie in JavaScript, i hope you can help me, as in topic, null property.

var add = document.getElementById('addition').checked;
var subs = document.getElementById('substraction').checked;
var multi = document.getElementById('multiplication').checked;
var div = document.getElementById('division').checked;

var result = 0;
    var x = parseInt(document.getElementById('firstNumber').value);
    var y = parseInt(document.getElementById('secondNumber').value);

function calculator() 
{
    if (add)
    {
        result = addition(x, y);
    }
    else if (subs)
    {
        result = substraction(x, y);
    }
    else if (multi)
    {
        result = multiplication(x, y);
    }
    else if (division)
    {
        result = division(x, y);
    };
}


<fieldset>
    <legend>Method</legend>
    <p><label><input type="radio" name="method" id="addition" />Addition</label></p>
    <p><label><input type="radio" name="method" id="substraction" />Substraction</label></p>
    <p><label><input type="radio" name="method" id="multiplication" />Multiplication</label></p>
    <p><label><input type="radio" name="method" id="division" />Division</label></p>
</fieldset>

<input type="submit" value="Submit" onclick="calculator();" />

他们我收到了消息未捕获的类型错误:无法读取空 index.html:24 的属性已检查"(匿名函数)"

And them i got message "Uncaught TypeError: Cannot read property 'checked' of null index.html:24 (anonymous function)"

请帮帮我.问候！

推荐答案

在页面上的 DOM 元素准备就绪之前，您的 javascript 代码正在执行.

Your javascript code is executing before the DOM elements are ready on the page.

您需要在 DOM 准备好后执行尝试获取输入的代码.

You need to execute the code that is trying to get the inputs after the DOM is ready.

(function () {
    if (window.addEventListener) {
        window.addEventListener('DOMContentLoaded', domReady, false);
    } else {
        window.attachEvent('onload', domReady);
    }
} ());

function domReady() {
    var add = document.getElementById('addition').checked;
    var subs = document.getElementById('substraction').checked;
    var multi = document.getElementById('multiplication').checked;
    var div = document.getElementById('division').checked;

    var result = 0;
    var x = parseInt(document.getElementById('firstNumber').value);
    var y = parseInt(document.getElementById('secondNumber').value);
}

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