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Loading and saving data

Ingvar Stepanyan edited this page Apr 12, 2014 · 7 revisions

In most cases you don't have binary data hard-coded in your JavaScript (why do you need any operation on it otherwise, eh?).

So you need to get this data from some external source and show result when you are done.

And jBinary provides following handy methods for those operations.

jBinary.loadData(source, [callback])

Loads data from given source and returns it in Promise or Node.js-like callback(error, data) if specified.

Source can be one of (if supported on current engine):

jBinary.load(source, [typeSet], [callback]):

Loads data from given source using jBinary.loadData, detects typeset using Repo associations if it's not specified explicitly, creates jBinary instance on this data and typeset and returns it in Promise or Node.js-like callback(error, data) if specified.

If Repo is not used, jBinary.load would accept only explicit typeset objects (no loading by name nor file format auto-detection).

saveAs(dest, mimeType = 'application/octet-stream', [callback])

Saves data to given destination and returns Promise or calls Node.js-like callback(error, data) if specified.

mimeType is set from given argument, typeSet['jBinary.mimeType'] directive or default to 'application/octet-stream' in order of precedence.

Destination can be one of (if supported on current engine):

  • File name to be used in browser "Save as" dialog (is shown to end user; old browsers might not use custom filename).
  • Node.js local file path.
  • Node.js Writable stream.

toURI(mimeType = 'application/octet-stream')

Returns URI suitable for usage in DOM elements (uses Blob URIs where supported, data-URIs in other cases, so may be problematic when creating from big data in old browsers).

Caveat

Please note that jBinary does not polyfill Promise in browsers but expects ES6 window.Promise or compliant polyfill (i.e., https://github.com/jakearchibald/es6-promise) to be available. In the case it's not, asynchronous methods (when called without Node.js-like callback) return simple object that just contains then(onFulfill, onReject) method and so can be used for handling result but can't be composed with another promises without corresponding cast operation supported by your library of choise (Promise.from(...), Q(...), etc.).

Example

fileInput.addEventListener('change', function () {
  jBinary.loadData(fileInput.files[0]).then(function (data) {
    if (error) {
      return console.log(error);
    }

    // here you get data from <input type="file" /> that you can use in jDataView/jBinary constructors
  });
});

jBinary.load('sample.tar').then(function (binary) {
  // here TAR format is auto-detected and used by `binary` (in the case you use it in combination with jBinary.Repo)
  var tar = binary.readAll;

  // ... more code ...

  return binary.saveAs('new.tar'); // opens browser's "Save as" dialog or saves to disk if called from Node.js
}).then(function () {
  console.log('Processed and saved successfully!');
}, function (err) {
  console.error(err);
});
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