var number1 = document.getElementById("queue");
height1 = number1.value+("px");queue is an input box, number1.value is its input value (a number), but the output of height1 is always px without any number.
for example:
console.log(number1.value); //20
console.log(height1);//pxI also tried a method
var number1 = document.getElementById("queue");
var number1Value = number1.value;
height1 = number1Value+("px");This time it’s even weirder,
console.log(number1.value);//20
console.log(number1Value);//console.log(number1.value.constructor == String);//trueProofnumber1.value is a string, then string plus string should be OK
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1. Probably what you understand
2. The correct way to obtain it
3. Another way to monitor the content in the input box
You are executing it when you open the page. The function is only executed once. When you enter the value again, you do not execute the method, and the first time the value is empty!
You need an event handling function. When the page is just loaded, the value must be empty, because you have not written a value in the input yet
var height = 0;
var input = document.querySelector('#input');
var btn = document.querySelector('#btn');
btn.addEventListener('click', function(){
}, false)