74 lines
2.6 KiB
JavaScript
74 lines
2.6 KiB
JavaScript
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/*
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Copyright (c) 2018 uupaa and 2019 Google LLC
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Use of this source code is governed by an MIT-style
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license that can be found in the LICENSE file or at
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https://opensource.org/licenses/MIT.
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*/
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/**
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* Creates a global function (defaulting to `self.__import__()`) that can
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* dynamically import modules. In browsers that support native dynamic
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* `import()`, the function defers to using that, otherwise a small polyfill
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* is used that creates a new module script and resolves once the module
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* is loaded.
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*
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* @param {Object} [options]
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* @param {string} [options.modulePath='.'] A path that relative import URLs
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* are resolved from. This is needed since this polyfill creates script
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* elements, and relative imports inside script elements will resolve
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* relative to the page URL. Set this option to have URLs resolve relative
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* to a different path (typically the location of your deployed modules
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* directory).
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* @param {string} [importFunctionName='__import__'] The name to use for the
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* global import function this polyfill will create. Since `import` is
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* a keyword in JavaScript, it's not possible to polyfill dynamic import
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* by creating a global function named `import()`. Thus, a different
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* name must be used.
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*/
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export function initialize({
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modulePath = '.',
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importFunctionName = '__import__',
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} = {}) {
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try {
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self[importFunctionName] = new Function('u', `return import(u)`);
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} catch (error) {
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const baseURL = new URL(modulePath, location);
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const cleanup = (script) => {
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URL.revokeObjectURL(script.src);
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script.remove();
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};
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self[importFunctionName] = (url) => new Promise((resolve, reject) => {
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const absURL = new URL(url, baseURL);
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// If the module has already been imported, resolve immediately.
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if (self[importFunctionName].moduleMap[absURL]) {
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return resolve(self[importFunctionName].moduleMap[absURL]);
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}
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const moduleBlob = new Blob([
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`import * as m from '${absURL}';`,
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`${importFunctionName}.moduleMap['${absURL}']=m;`,
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], {type: 'text/javascript'});
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const script = Object.assign(document.createElement('script'), {
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type: 'module',
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src: URL.createObjectURL(moduleBlob),
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onerror() {
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reject(new Error(`Failed to import: ${url}`));
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cleanup(script);
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},
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onload() {
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resolve(self[importFunctionName].moduleMap[absURL]);
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cleanup(script);
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},
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});
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document.head.appendChild(script);
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});
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self[importFunctionName].moduleMap = {};
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}
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}
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