image-blobber

A small module for reading image file base64/dimensions, and scaling them to a max height or width.

Installation

image-blobber can be installed from npm.

npm install --save image-blobber

//ES6
import * as imageblobber from "image-blobber";
 
//Node-style require
const imageblobber = require("image-blobber");

Usage

All image-blobber functions are promisified.

Supported: boolean

An exported boolean that indicates whether the current environment supports the FileReader needed by the getFileBlobs function. If false, getFileBlobs will throw an error.

import {Supported} from "image-blobber";
 
if (!Supported)
{
    throw new Error("Your browser does not support the FileReader API.");
}

getFileBlobs(input: HtmlInputElement): Promise<File[]>

Gets all file blobs for an HTML5 file input element.

import {getFileBlobs} from "image-blobber";
 
const input = document.getElementById("my-file-input");
 
getFileBlobs(input).then((blobs) =>
{
    console.log(blobs.length); // 3
});

getBase64(file: File): Promise<BlobDetails>

Gets the base64 string, filename and dimensions for the given image file. See below for the BlobDetails interface.

import {getBase64} from "image-blobber";
 
const file: File = ...;
 
getBase64(file).then((details) =>
{
    console.log(details.filename);   // "my-file.png"
    console.log(details.base64);     // "data:image/png;base64,..."
    console.log(details.dimensions); // { height: 150, width: 75 }
});

scaleBase64(base64: string, options: ScaleOptions): Promise<ScaleResult>

Scales a base64 image string according to the options passed in. See below for the ScaleOptions and ScaleResult interfaces.

import {scaleBase64} from "image-blobber";
 
const base64: string = ...;
 
scaleBase64(base64, {height: 400, width: 400, preserveRatio: true}).then((scaledImage) =>
{
    console.log(scaledImage.scaledBase64);     // "data:image/png;base64,..."
    console.log(scaledImage.scaledDimensions); // { height: 150, width: 75 }
});

Tie it all together

import * as Promise from "bluebird";
import * as blobber from "file-blobber";
 
const input = document.querySelector("input") as HTMLInputElement;
 
blobber.getFileBlobs(input)
    .then((blobs) =>
    {
        return Promise.all(blobs.map(blob => blobber.getBase64(blob)));
    })
    .then((images) =>
    {
        return Promise.all(images.map(i => blobber.scaleBase64(i.base64, {height: 400, width: 400, preserveRatio: true})));
    })
    .then((scaledImages) =>
    {
        // Do something with the scaled images.
    })

Interfaces

The following interfaces are used or returned at some point by image-blobber. If you're using Typescript, the compiler should automatically pick up these definitions when image-blobber is installed.

Dimensions

Property	Type	Comments
height	number	The image's height.
width	number	The image's width.

BlobDetails

Property	Type	Comments
filename	string	The name of the file as it appears on the user's machine.
base64	string	A base64 string representing the image. Can be set as an <img /> element's src.
dimensions	Dimensions	The image's height and width dimensions.

ScaleResult

Property	Type	Comments
scaledBase64	string	A base64 string representing the scaled image. Can be set as an <img /> element's src.
scaledDimensions	Dimensions	The scaled image's new height and width dimensions.

ScaleOptions

Property	Type	Comments
height	number	The maximum height allowed for a scaled image. Optional, but options must include either a height or width.
width	number	The maximum width allowed for a scaled image. Optional, but options must include either a height or width.
preserveRatio	boolean	Whether aspect ratio should be preserved. If true, image will be scaled to an aspect ratio that satisfies both height and width. Default true.