Get input text width when typing

问题:

I have a input type text

<input type="text" id="txtid">

When i start typing text inside input, i should be able to get the lenght of the entered text.

This is what I tried:

document.getElementById("txtid").offsetWidth;

and

var test = document.getElementById("txtid");
var width = (test.clientWidth + 1) + "px";

These two does not give the width of the text entered

Basically what I want is:

For suppose input text width is 320px. I need the width of the entered text i.e 120px, which keeps on changing when I enter.

回答1:

I see two ways.

First:

You can use a div with content editable instead input. Like this you can see the width of the div.

var elemDiv = document.getElementById('a');

elemDiv.onblur = function() {
  console.log(elemDiv.clientWidth + 'px');
}

div {
  width: auto;
  display: inline-block;
}

<div id='a' contenteditable="plaintext-only">Test</div>

Note : Like @Leon Adler say, this way allows pasting images, tables and formatting from other programs. So you maybe need some validation with javascript to check the content before get the size.

---

Second:

Use an input type text and past the content into an invisible div. And you can see the width of the invisible div.

var elemDiv = document.getElementById('a'),
  elemInput = document.getElementById('b');

elemInput.oninput = function() {
  elemDiv.innerText = elemInput.value;
  console.log(elemDiv.clientWidth + 'px');
}

.div {
  width: auto;
  display: inline-block;
  visibility: hidden;
  position: fixed;
  overflow:auto;
}

<input id='b' type='text'>
<div id='a' class='div'></div>

Note : For this way, you must have the same font and font size on input and div tags.

回答2:

I have modified Chillers answer slightly, because it looks like you wanted the width rather than the letter count. I have created a span, which is absolute positioned off the screen. I am then adding the value of the input to it and then getting the width of the span. To make it more fancy you could create the span with javascript.

Note that the input and the span would have to have the same CSS styling for this to be accurate.

document.getElementById("txtid").addEventListener("keyup", function(){
  var mrspan = document.getElementById("mrspan");
  mrspan.innerText = this.value;
  console.log(mrspan.offsetWidth + "px");
});

<input type="text" id="txtid">
<span id="mrspan" style="position:absolute;left:-100%;"></span>

回答3:

UPDATE

Two things I want to put forward

• Doing display none will not give you any offsetWidth if we are trying using vanilla JS. we can use visibility: hidden; or opacity:0 for that.

• we need to add overflow:auto to the hidden span or else the text will be warped to the next line if it exceeds the browser window width and the width will stay fixed (width of window)

OLD

You can try this approach

Add a span and hide it

<span id="value"></span>

and then onkeyup add the text of the textfield on your hidden span and get its width.

WITH THE HELP OF JQUERY

SNIPPET (UPDATED)

function update(elm,value) {
     $('#value').text(value);
     var width =   $('#value').width();
     $('#result').text('The width of '+ value +' is '+width +'px');
   
}

#value{
  display:none;
  overflow:auto;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<input type="text" oninput='update(this,this.value)'>
<span id="value"></span>
<div id="result"></div>

USING JS ONLY

SNIPPET (UPDATED)

function update(elm,value) {
     var span = document.getElementById('value');
     span.innerHTML = value;    
     var width = span.offsetWidth;
     document.getElementById('result').innerHTML = 'The width of '+ value +' is '+ width+ 'px';
   
}

#value{
  opacity:0;
  overflow:auto;
}

<input type="text" oninput='update(this,this.value)'>
<span id="value"></span>
<div id="result"></div>

回答4:

Canvas measureText() method can be helpful in such a case. Call the following function whenever you need to get your text width:

function measureMyInputText() {
    var input = document.getElementById("txtid");
    var c = document.createElement("canvas");
    var ctx = c.getContext("2d");
    var txtWidth = ctx.measureText(input.value).width;

    return txtWidth;
}

For more accurate result, you may set font styling to the canvas, especially if you set some font properties to the input. Use the following function to get the input font:

 function font(element) {
     var prop = ["font-style", "font-variant", "font-weight", "font-size", "font-family"];
     var font = "";
     for (var x in prop)
         font += window.getComputedStyle(element, null).getPropertyValue(prop[x]) + " ";

     return font;
 }

Then, add this line to the frist function:

ctx.font = font(input);

回答5:

Using the above solution, I turned it into a single function.

let getWidth = (fontSize, value) => {
  let div = document.createElement('div');
  div.innerHTML = value;
  div.style.fontSize = fontSize;
  div.style.width = 'auto';
  div.style.display = 'inline-block';
  div.style.visibility = 'hidden';
  div.style.position = 'fixed';
  div.style.overflow = 'auto';
  document.body.append(div)
  let width = div.clientWidth;
  div.remove();
  return width;
};
getWidth('10px', 'test');