Suppose, I'm not sure if the selected authorities exist (but if they do, I want them selected). If there are no authorities selected, I want jQuery to select the authorities regardless of whether they are selected (actually, this means retrieving the value of the hidden input). My thoughts on using JS's "true value"/"false value" concept to handle this situation are:
let user = {
id: $(this).find('[name=id]').val(),
username: $(this).find('[name=username]').val(),
password: $(this).find('[name=password]').val(),
name: $(this).find('[name=name]').val(),
lastName: $(this).find('[name=lastName]').val(),
department: $(this).find('[name=department]').val(),
salary: $(this).find('[name=salary]').val(),
age: $(this).find('[name=age]').val(),
email: $(this).find('[name=email]').val(),
enabledByte: $(this).find('[name=enabledByte]').val(),
authorities: JSON.parse($(this).find('[name=authorities]:checked').val()) ||
JSON.parse($(this).find('[name=authorities]').val())
};
However, it doesn't work. Interestingly, it does work in the code snippet below. Isn't the undefined returned by val() when the match fails a "false value"? think about it! My best guess is that JSON.parse() throws an error when undefined is parsed, rather than returning some "false value" as I would expect. This method doesn't accept "param OR param", right?
How do you think I should provide a fallback for this situation (besides, of course, checking the selected authorities individually for a "false value", which is a bit verbose for me) ?
<头>
<元字符集=“UTF-8”>
<标题>Management Page
<正文>
<标题>
name
Surname
department
e-mail
<正文>
John
U.S. Department of Energy
IT
john_d@gmail.com
simple
U.S. Department of Energy
human Resources
jane_d@gmail.com
Fill in the form
<表格>
<标签=“名称”>name:
<脚本>
$(document).ready(function() {
$('form').on('submit', asynchronous function (event) {
event.preventDefault();
$('tbody').append(
`
${$(this).find('[name=name]').val()}
${$(this).find('[name=last-name]').val()}
${$(this).find('[name=department]').val()}
${$(this).find('[name=email]').val() || 'Not applicable'}
`
);
const SubmitButton = $(this).find('[type=submit]');
Constant form = $(this);
Submit button.removeClass('btn-primary')
.addClass('btn-success')
.attr('value', 'User has been added!')
.attr('type', 'button')
.click(() => $('[href="#users-table"]').tab('show'));
setTimeout(function(){
commitButton.removeClass('btn-success')
.addClass('btn-primary')
.attr('value', 'submit')
.attr('Type
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
The problem is that if the selector doesn't find any matches,
.val()returnsundefined, whileJSON.parse(undefined)throws an exception .Execute the fallback in the parameter list of
JSON.parse()so that you will parse any value that is successfully obtained.authorities: JSON.parse($(this).find('[name=authorities]:checked').val() || $(this).find('[name=authorities]:first').val())Depending on your use case, you have several options:
JSON.parselike this. This will make it fall back to other strings before parsing, so it won't error if the first value isundefined. However, this will result in an error if both values areundefinedor one of them is invalid JSON.JSON.parse($(this).find('[name=authorities]:checked').val()) || $(this).find('[name=authorities]').val());undefined, you can fall back tonull.nullis a valid JSON value and can be parsed. However, if any of the values are invalid JSON, an error will still occur.JSON.parse($(this).find('[name=authorities]:checked').val()) || $(this).find('[name=authorities]').val() || null);// Helper to make it easier to do this inline function safeJsonParse(string) { try { return JSON.parse(string); } catch { // JSON is invalid. Will implicitly return undefined. } } safeJsonParse($(this).find('[name=authorities]:checked').val()) || safeJsonParse($(this).find('[name=authorities]').val())