如何计算 javascript 中带前导零的数字的位数？

Question

I am taking a field value, that should be a 4 digit number.

I want to make sure that the value is a 4 digit number and if not, have a pop up that says "enter a 4 digit number".

I noticed that when I put the field value into a variable it does not take any of the leading zeros. The last test case I ran the code with was a value of '0000'.

var relay = this.getField("RELAY NUM").value;
var relayString = relay.toString();
var relaySplit = relayString.split("");
    
console.println("relay= " + relay);
console.println("string= " + relayString);
console.println("split= " + relaySplit);
    
for(i = 0; i < 4; i++){
    if (relaySplit[i] >= 0) {
        console.println("Looks good so far");
    } else {
        console.println("Please enter 4 digit number");
    }
}

--------------------------------------------------------
relay= 0
string= 0
split= 0
Looks good so far
Please enter 4 digit number
Please enter 4 digit number
Please enter 4 digit number

true

Answer 1

Instead of traversing arrays, an approach you may want to consider is using a regex to determine whether the input value meets your criteria. Then on events such as keyup (using jQuery here but not necessary), you run the validation and apply styles, or send forth the popups as you wish. I put a limit on the length of the input so users are not able to enter MORE then expected input, but this isn't necessarily needed.

 $("#input").keyup(function() { let input = $("#input").val() let isValid = validate(input) $("#val").text(isValid? "Valid": "Invalid") }) function validate(val) { let x = /^[0-9]{4}$/ return x.test(val) }

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <div> <input type="text" id="input" maxLength="4" /> <label id="val"></label> </div>