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how to reset canvas object height based on the content height?

I m drawing text content on the canvas which is dynamically generated but I cant able to estimate the height the content occupies within the canvas as resetting the canvas height will reset the canvas. How can I resize the canvas based on the height of the content it draws so that the content is accumulated exactly.

Presenting complex tabular text as an inaccesible canvas image is a terrible usability mistake. However if you must you can use the table as an image. You can get the with and height of the image and set the size of your canvas. Finaly you draw the image on the canvas.
var img = new Image();
img.src = whatever;
img.onload = function() {
//get the with and height of the image
var w = img.width;
var h = img.height;
// set the canvas width and height
canvas.width = w;
canvas.height= h;
// draw the image
ctx.drawImage( img, 0, 0, w, h );

Resize image and rotate canvas 90 degrees

There's quite a few topics here about rotating images with canvas on js. I read most of them, and couldn't figure out a solution for my problem.
I'm receiving an image (from an upload component) of whatever resolution. I'm resizing it to 1024x768 like:
var canvas = document.createElement('canvas');
var ctx = canvas.getContext("2d");
if (img.width >= img.height) {
canvas.width = 1024;
canvas.height = 768;
} else {
canvas.width = 768;
canvas.height = 1024;
}
ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
It works fine.
But on Safari/iOs, when I take a picture and upload, the image has ALWAYS a higher width value than height, so the code above doesn't work.
So I decided to use exif-js to detect the image's orientation. When the Orientation attribute is higher than 4, I need to rotate the image 90 degrees, and swap height and width values.
I tried to rotate the image like this:
canvas.width = 768; // swapping values
canvas.height = 1024;
ctx.translate(canvas.width/2, canvas.height/2); // translate to center
ctx.rotate(Math.PI/2); // rotate 90 degrees
ctx.drawImage(img, -img.width/2,-img.height/2); // not sure of the dx and dy values here...
The image is rotated. But it has taken just a small portion of the original image to display on the canvas, so it feels "zoomed in"... it seems that I'm using the wrong values on the drawImage method, but not sure how to fix.
How can I fix this rotation with fixed height and width values?

To rotate 90 deg clockwise on a new canvas.
const canvas = document.createElement("canvas");
canvas.width = image.height;
canvas.height = image.width;
const ctx = canvas.getContext("2d");
ctx.setTransform(
0,1, // x axis down the screen
-1,0, // y axis across the screen from right to left
image.height, // x origin is on the right side of the canvas
0 // y origin is at the top
);
ctx.drawImage(image,0,0);
ctx.setTransform(1,0,0,1,0,0); // restore default
If you need to scale the image to fit a size (assuming image will be rotated)
const width = 1024; // after rotation
const height = 768; // after rotation
const scale = width / image.height; // how much to scale the image to fit
const canvas = document.createElement("canvas");
canvas.width = width;
canvas.height = height;
const ctx = canvas.getContext("2d");
ctx.setTransform(
0,scale, // x axis down the screen
-scale,0, // y axis across the screen from right to left
width, // x origin is on the right side of the canvas
0 // y origin is at the top
);
ctx.drawImage(image,0,0);
ctx.setTransform(1,0,0,1,0,0); // restore default

HTML flexible canvas scale

I am making a website which will load some blueprint images on a canvas.
but the images are vary in height and width.i Would like to make the canvas scaling equal to the uploaded image scale. How do i code to make the canvas width and height changeble respective to uploaded image.
This done in html5

If I understand you correctly, you want to load images with various dimensions. According to the dimension, set the width / height of the canvas and draw the image?
In that case you could add an eventListener to the image. Once it's loaded, get the width and height. Use those to set the dimensions of the canvas. After that, draw the image on the canvas.
var image = new Image();
image.addEventListener('load', function(e) {
var width = image.width;
var height = image.height;
var canvas = document.querySelector('canvas');
canvas.width = width;
canvas.height = height;
canvas.getContext('2d').drawImage(image, 0, 0, width, height);
});
image.src = 'https://upload.wikimedia.org/wikipedia/commons/c/c4/PM5544_with_non-PAL_signals.png';
<canvas></canvas>
Fiddle

var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext('2d');
var imageObj = new Image();
imageObj.src = 'images/e1.jpg';
canvas.width = imageObj.naturalWidth;
canvas.height = imageObj.naturalHeight;
this also works

resize an image using canvas

Hi want to resize an image using canvas but can't get it to work...
I want the image to be 100px * 100px, is there any way to solve this?
I have tried googleing and trying but can't get it to work...
I also tried changing the img size in css but this doesn't help either, please help me!
function getBase64Image(img) {
// Create an empty canvas element
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
canvas.width = img.width;
canvas.height = img.height;
// Copy the image contents to the canvas
ctx.drawImage(img, 0, 0);
// Get the data-URL formatted image
// Firefox supports PNG and JPEG. You could check img.src to guess the
// original format, but be aware the using "image/jpg" will re-encode the image.
var dataURL = canvas.toDataURL("image/png");
return dataURL.replace(/^data:image\/(png|jpg);base64,/, "");
}
I also realized that I need to rotate it how can I do this?

You have to get a ratio of the width and apply it to the height.
var ratio = 100 / img.width; // 100 for desired width in px
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
ctx.drawImage(img, 0,0, canvas.width, canvas.height);
typed on phone so forgive small mistakes.

Can i change the image size inside a canvas element?

I want to have an image inside a canvas element. The canvas will have static size (e.g 800x600) but the Image can be larger or smaller. So if the Image is smaller there will be white area round the image, if it is larger the image will not fit the canvas so some parts of the image won't be visible. What i want to ask is the following. Can I resize the image to fit canvas (e.g after user input) after the image has rendered on canvas?
html
<canvas id="myCanvas" width="800" height="600">
js
canvas = document.getElementById('myCanvas');
context = canvas.getContext('2d');
image = new Image();
image.src = 'url_to_image';
//lets say image is 400x300;
//will this work too?
image.width = image.width*2;
image.height = image.height * 2;
context.drawImage(image, 0, 0);
//or should i use this?
//context.drawImage(image, 0, 0, image.width*2, image.height * 2);
The second one stretches the image to fit the canvas. Can I stretch the image before calling drawImage (by editing image.width and image.height)? I have seen some editing software that zooms on the image and canvas stays static, without changing its size.

Not correct:
image.width = image.width*2;
image.height = image.height * 2;
context.drawImage(image, 0, 0);
as image's width and height properties are read-only.
Correct:
context.drawImage(image, 0, 0, image.width*2, image.height * 2);
Here is another way to make the image fit the canvas independent on aspect ratio:
Simulation background-size: cover in canvas