I am encountering an issue with the code below:
<input type="text" value="123" id="txtbox">
<script>
var myVar = document.getElementById('txtbox').value;
if (myVar.substring) {
alert('string');
} else{
alert('number');
}
</script>
Regardless of the value entered in the textbox, it always triggers the alert message as string. Is there a solution to modify the code so that entering a number in the textbox will trigger the alert message as number instead of string? Thank you.
When dealing with <code>input elements, it is important to remember that the value is always a string, which may consist of digits.
If you need to determine if the string contains valid numbers, you will need to parse it and establish your criteria for what constitutes a valid number.
Various methods such as parseInt(myVar), +myVar, isNaN(myVar), and Number(myVar) are commonly suggested, but there are limitations:
parseInt only parses the beginning of the string, so parseInt("345foo") would result in 345
parseInt is only suitable for whole numbers, while parseFloat should be used for numbers with fractional parts
These methods do not recognize thousands separators
These methods do not handle decimal separators other than ., which may vary in different regions
+myVar, Number(myVar), and isNaN(myVar) consider an empty string as 0
Therefore, it is necessary to preprocess the string based on the desired input conditions.
Once the format(s) are determined, there are several resources available for guidance on parsing, such as:
Determines if a value is not a number using the isNaN function:
var myVar = document.getElementById('txtbox').value;
var myNum = +myVar;//suggested method by T.J.
if (isNaN(myNum)) {
alert('This is a string.');
} else{
alert('This is a number.');
}
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