通用解决方案无需配置，自动检测所有输入修改，包括可满足的元素:

"use strict";
(() => {
const modified_inputs = new Set;
const defaultValue = "defaultValue";
// store default values
addEventListener("beforeinput", (evt) => {
    const target = evt.target;
    if (!(defaultValue in target || defaultValue in target.dataset)) {
        target.dataset[defaultValue] = ("" + (target.value || target.textContent)).trim();
    }
});
// detect input modifications
addEventListener("input", (evt) => {
    const target = evt.target;
    let original;
    if (defaultValue in target) {
        original = target[defaultValue];
    } else {
        original = target.dataset[defaultValue];
    }
    if (original !== ("" + (target.value || target.textContent)).trim()) {
        if (!modified_inputs.has(target)) {
            modified_inputs.add(target);
        }
    } else if (modified_inputs.has(target)) {
        modified_inputs.delete(target);
    }
});
// clear modified inputs upon form submission
addEventListener("submit", (evt) => {
    modified_inputs.clear();
    // to prevent the warning from happening, it is advisable
    // that you clear your form controls back to their default
    // state with evt.target.reset() or form.reset() after submission
});
// warn before closing if any inputs are modified
addEventListener("beforeunload", (evt) => {
    if (modified_inputs.size) {
        const unsaved_changes_warning = "Changes you made may not be saved.";
        evt.returnValue = unsaved_changes_warning;
        return unsaved_changes_warning;
    }
});
})();

你可以在这里查看详细的解释: http://techinvestigations.redexp.in/comparison-of-form-values-on-load-and-before-close/

主要代码:

function formCompare(defaultValues, valuesOnClose) {
 
    // Create arrays of property names
    var aPropsFormLoad = Object.keys(defaultValues);
    var aPropsFormClose = Object.keys(valuesOnClose);
 
    // If number of properties is different,
    // objects are not equivalent
    if (aPropsFormLoad.length != aPropsFormClose.length) {
        return false;
    }
 
    for (var i = 0; i < aPropsFormLoad.length; i++) {
        var propName = aPropsFormLoad[i];
 
        // If values of same property are not equal,
        // objects are not equivalent
        if (defaultValues[aPropsFormLoad]+"" !== valuesOnClose[aPropsFormLoad]+"") {
            return false;
        }
    }
 
    // If we made it this far, objects
    // are considered equivalent
    return true;
 
}

//add polyfill for older browsers, as explained on the link above

//use the block below on load
    for(i=0; i < document.forms[0].elements.length; i++){
    console.log("The field name is: " + document.forms[0].elements[i].name +
        " and it’s value is: " + document.forms[0].elements[i].value );
    aPropsFormLoad[i] = document.forms[0].elements[i].value;
    }

//create a similar array on window unload event.

//and call the utility function
    if (!formCompare(aPropsOnLoad, aPropsOnClose))
    {
    //perform action: 
    //ask user for confirmation or
    //display message about changes made
    }

查看JavaScript onbeforeunload事件。它是微软引入的非标准JavaScript，但是它可以在大多数浏览器中运行，他们的onbeforeunload文档有更多的信息和示例。

通用解决方案无需配置，自动检测所有输入修改，包括可满足的元素:

"use strict";
(() => {
const modified_inputs = new Set;
const defaultValue = "defaultValue";
// store default values
addEventListener("beforeinput", (evt) => {
    const target = evt.target;
    if (!(defaultValue in target || defaultValue in target.dataset)) {
        target.dataset[defaultValue] = ("" + (target.value || target.textContent)).trim();
    }
});
// detect input modifications
addEventListener("input", (evt) => {
    const target = evt.target;
    let original;
    if (defaultValue in target) {
        original = target[defaultValue];
    } else {
        original = target.dataset[defaultValue];
    }
    if (original !== ("" + (target.value || target.textContent)).trim()) {
        if (!modified_inputs.has(target)) {
            modified_inputs.add(target);
        }
    } else if (modified_inputs.has(target)) {
        modified_inputs.delete(target);
    }
});
// clear modified inputs upon form submission
addEventListener("submit", (evt) => {
    modified_inputs.clear();
    // to prevent the warning from happening, it is advisable
    // that you clear your form controls back to their default
    // state with evt.target.reset() or form.reset() after submission
});
// warn before closing if any inputs are modified
addEventListener("beforeunload", (evt) => {
    if (modified_inputs.size) {
        const unsaved_changes_warning = "Changes you made may not be saved.";
        evt.returnValue = unsaved_changes_warning;
        return unsaved_changes_warning;
    }
});
})();

下面的一句话对我很管用。

window.onbeforeunload = s => modified ? "" : null;

根据应用程序的状态将modified设置为true或false。

我做了不同的，分享在这里，以便有人可以得到帮助，只测试Chrome。

我想警告用户关闭标签只有当有一些变化。

<input type="text" name="field" value="" class="onchange" />

var ischanged = false;

$('.onchange').change(function () {
    ischanged = true;
});

window.onbeforeunload = function (e) {
    if (ischanged) {
        return "Make sure to save all changes.";
    }        
};

工作很好，但有一个其他的问题，当我提交的形式，我得到不想要的警告，我看到了很多解决方法，这是因为onbeforeunload火灾之前onsubmit，这就是为什么我们不能处理它在onsubmit事件像onbeforeunload = null，但onclick事件提交按钮火灾前这两个事件，所以我更新了代码

var isChanged = false;
var isSubmit = false;

window.onbeforeunload = function (e) {
    if (isChanged && (!isSubmit)) {
        return "Make sure to save all changes.";
    }        
};

$('#submitbutton').click(function () {
    isSubmit = true;
});

$('.onchange').change(function () {
    isChanged = true;
});