在Javascript中使用文本框的“ .value”属性

Question

document.getElementById("t3").value = document.getElementById("t1").value + 
                                      document.getElementById("t2");

Through above code I could not get the result of addition of two numbers.

Answer 1

If you want to add those to values, you have to convert them to integer at first. .value always holds a string.

parseInt(document.getElementById("t1").value, 10) + parseInt(document.getElementById("t2").value, 10);

Answer 2

You are not actually adding two numbers together. You are attempting to add document.getElementById("t1").value (which is a string containing with numbers in it) to document.getElementById("t2") , which is a DOM element.

You probably get a result like this:

43[object HTMLInputElement]

You need to (a) get the value property of the second element and (b) add them together as numbers, rather than as strings.

document.getElementById("t3").value = (+document.getElementById("t1").value) + 
                                      (+document.getElementById("t2").value);

(+document.getElementById("t1").value) converts the value into a number. It is the unary plus + operator .

Answer 3

Try this:

document.getElementById("t3").value = parseInt(document.getElementById("t1").value,10) + 
                                  parseInt(document.getElementById("t2").value,10);

Answer 4

This is cheeky, but on the off-chance the t3 element that the OP is trying to update is a div or span rather than an input :)

var t1, t2, t3;

t1 = document.getElementById("t1");
t2 = document.getElementById("t2");
t3 = document.getElementById("t3");

t3.innerHTML = parseInt(t1.value, 10) + parseInt(t2.value, 10);

Or

t3.innerHTML = +t1.value + +t2.value;