Related to this question here. Can I check if an element in the DOM has a value or not? I'm trying to put it into an 'if' statement and not sure if my approach is correct. Here goes:
if (document.getElementById('customx')){
//do something
}
Or should it be:
if (document.getElementById('customx') == ""){
//do something
}
EDIT: By value I mean, customx is a text input box. How can I check if this field has no text entered.
The getElementById method returns an Element object that you can use to interact with the element. If the element is not found, null is returned. In case of an input element, the value property of the object contains the string in the value attribute.
By using the fact that the && operator short circuits, and that both null and the empty string are considered "falsey" in a boolean context, we can combine the checks for element existence and presence of value data as follows:
var myInput = document.getElementById("customx");
if (myInput && myInput.value) {
alert("My input has a value!");
}
getElementById will return false if the element was not found in the DOM.
var el = document.getElementById("customx");
if (el !== null && el.value === "")
{
//The element was found and the value is empty.
}
var input = document.getElementById("customx");
if (input && input.value) {
alert(1);
}
else {
alert (0);
}
Empty is not the same as "no value".
HTMLInputElement.value is '' when you have an invalid entry. If .value is not '', then it's not empty. That's definite, but since there are times when .value === '' but not empty, we need to test. For example, in Chrome, with a number input type, if you type . or e it will be placed in the input box, but .value will not change from '' because it's invalid.
<input type=number>
We can ask the browser for more information and thankfully ValidityState is extremely well supported. Basically, if there's no value, but the browser says there's a bad input, then it's not empty.
function isInputEmpty(input) {
return !input.value && !input.validity.badInput;
}
Edit: Credits to @osullic for find this in spec:
A control's value is its internal state. As such, it might not match the user's current input.
https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#a-form-control's-value
HTMLInputElement.value doesn't change from '' unless what's been entered passes validation.
HTMLInputElement with Web Components and am trying to closely follow spec. There's a way to detect with :placeholder-shown, but you need a placeholder (even if blank) and then that can affect text selection. badInput seems more compatible.Your first one was basically right. This, FYI, is bad. It does an equality check between a DOM node and a string:
if (document.getElementById('customx') == ""){
DOM nodes are actually their own type of JavaScript object. Thus this comparison would never work at all since it's doing an equality comparison on two distinctly different data types.
You want:
if (document.getElementById('customx').value === ""){
//do something
}
The value property will give you a string value and you need to compare that against an empty string.
" " is different to "" but hard to spot on screen.var myInput = document.getElementById("customx");
if (myInput.value.length > 0) {
//do something;
}
(.length > 0 is another way to check the input element)
valueattribute?<input type="text" value="myValue">or<span>myValue</span>?