Javascript HTML选择永久显示值?
如何使下拉选择框始终显示相同的值,而不是选定的值 例如:Javascript HTML选择永久显示值?,javascript,html,css,Javascript,Html,Css,如何使下拉选择框始终显示相同的值,而不是选定的值 例如: <select value="Color"> <option value="blue">Blue</option> <option value="red">Red</option> </select> 蓝色 红色 我希望选择框在被选中时总是显示“颜色”,而不是“蓝色”或“红色” 以下是代码: <select> <option value="co
<select value="Color">
<option value="blue">Blue</option>
<option value="red">Red</option>
</select>
蓝色
红色
我希望选择框在被选中时总是显示“颜色”,而不是“蓝色”或“红色” 以下是代码:
<select>
<option value="color" selected>Color</option>
<option value="blue">Blue</option>
<option value="red">Red</option>
</select>
颜色
蓝色
红色
您可以将
selected
属性添加到第一个选项中,该选项现在将是color
,希望这有所帮助。鉴于您能够接受JavaScript解决方案,如中所述,我可以为您提供以下解决方案,该解决方案应具有一定的可扩展性,并可根据您的需要进行定制
不过,它可以简化,这可能对任何(潜在)未来用户都有好处:
// simple function to uppercase the first letter of a given string,
// if it's a lower-case letter:
// of a given string:
function upperCaseFirst(str) {
return str.replace(/^[a-z]/, function (firstLetter) {
return firstLetter.toUpperCase();
});
}
// as above, but from upper-case to lower-case:
function lowerCaseFirst(str) {
return str.replace(/^[A-Z]/, function (firstLetter) {
return firstLetter.toLowerCase();
});
}
function showOptionString(opts) {
/* these are the defaults,
replace: Boolean, true/false
true - replaces the option-text with the
supplied prefix/suffix strings
false - wraps the option-text with the
supplied prefix/suffix strings
sentenceCaseOption: Boolean, true/false
true - lower-cases both the first letter of
the option-text, and the first-letter
of the option's original text when
constructing the new text
false - maintains both the option-text's case
and that of the supplied prefix-string
separator: String,
the string with which the option-text should be
separated from the supplied prefix/suffix
prefixString: String,
the text which will precede the option-text (if
settings.replace is set to false), or which will
replace the option-text (by default)
suffixString: String,
the text which will follow the option-text (if
settings.replace is set to false), or which will
replace the option-text (by default)
var settings = {
'replace': true,
'sentenceCaseOption': true,
'separator': ' ',
'prefixString': '',
'suffixString': ''
};
// if the user has supplied options:
if (opts) {
// we iterate through the properties of the settings object and
for (var prop in settings) {
// if the property is of the object itself (not from
// elsewhere in the prototype chain)
if (settings.hasOwnProperty(prop)) {
// overwrite the property of the settings object,
// if that property is not undefined in the supplied
// options object (otherwise we 'retain' the default):
settings[prop] = opts[prop] !== undefined ? opts[prop] : settings[prop];
}
}
}
// having used Function.prototype.call when assigning the
// the event-handler, 'this' is the <select> element:
var select = this,
// retrieving the <option> elements from the <select>
options = select.options,
// finding the selected <option>
selected = options[select.selectedIndex],
// we use String.prototype.trim() later to remove
// leading/trailing white-space from the option-text;
// here we create a regular expression to remove non white-
// space portions of the supplied separator string.
// removing leading white-space from the separator
// ' : ' would become ': '
leading = settings.separator.replace(/^\s+/, ''),
// removing trailing white-space from the separator
// ' : ' would become ' :'
trailing = settings.separator.replace(/\s+$/, ''),
// creating a single regular expression, using the 'new RegExp()'
// constructor which will match the above strings when found
// at the beginning (leading) or end (trailing) of the
// option-text:
trimReg = new RegExp('^' + leading + '|' + trailing + '$', 'g');
// using forEach to iterate over the array-like NodeList of
// <option> elements:
Array.prototype.forEach.call(options, function (opt) {
// opt is the current <option> of the NodeList over
// which we're iterating.
// creating a property on the Node, setting its 'oldValue' property
// to be equal to its oldValue property or, if not yet set, to its
// current text:
opt.oldValue = opt.oldValue || opt.text;
// setting the text back to its oldValue (this is to revert
// previously-changed text back to its original form):
opt.text = opt.oldValue;
});
// if settings.replace is true:
if (settings.replace) {
// we set the selected-option's text to a string created by
// joining an Array of the prefixString and suffixString
// together with the separator string:
selected.text = [settings.prefixString, settings.suffixString].join(settings.separator);
} else {
// otherwise, if sentenceCaseOption is true:
if (settings.sentenceCaseOption) {
// do much the same, except we include the option-text's
// lower-cased oldValue in the string we create:
selected.text = [settings.prefixString, lowerCaseFirst(selected.oldValue), settings.suffixString].join(settings.separator);
} else {
// and, if we don't need/want to sentence-case the
// option text we do exactly the same as above, but
// without calling lowerCaseFirst() on the oldValue:
selected.text = [settings.prefixString, selected.oldValue, settings.suffixString].join(settings.separator);
}
}
// here we get the selected-option's text, trim the
// leading/trailing white-space from it and replace any
// remaining portions of the separator that might exist.
// if settings.sentenceCaseOption is true,
// we use upperCaseFirst() to upper-case the first-letter,
// otherwise we do not:
selected.text = settings.sentenceCaseOption ? upperCaseFirst(selected.text.trim().replace(trimReg, '')) : selected.text.trim().replace(trimReg, '');
}
// a reference to the first <select> element from the document:
var select = document.querySelector('select');
// adding a 'change' event-listener to the <select> element:
select.addEventListener('change', function () {
// assigning the showOptionString() function as
// the event-handler, together with Function.prototype.call
// to pass the <select> element to the function, inside of
// of which it will be the function's 'this':
showOptionString.call(this, {
// setting some of the user-supplied options:
'prefixString': 'color',
'suffixString': '',
'separator': ' - '
});
});
蓝色
红色
我希望用户能够选择值(更改所选文本的颜色),但我希望显示的值始终为“颜色”我认为如果没有JavaScript,这是不可能的。这应该通过在
之外添加
来解决,而不是试图让下拉列表成为它自己的标签。我可以使用JavaScript来实现这一点。问题是,在用户选择其他选项后,如何显示“颜色”。它不是询问如何设置默认选项。