react-native/Libraries/Utilities/truncate.js

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/**
* Copyright (c) 2015-present, Facebook, Inc.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
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*
* @format
* @flow
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*/
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'use strict';
type truncateOptions = {
breakOnWords: boolean,
minDelta: number,
elipsis: string,
};
const defaultOptions = {
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breakOnWords: true,
minDelta: 10, // Prevents truncating a tiny bit off the end
elipsis: '...',
};
// maxChars (including ellipsis)
const truncate = function(
str: ?string,
maxChars: number,
options?: truncateOptions,
): ?string {
options = Object.assign({}, defaultOptions, options);
if (
str &&
str.length &&
str.length - options.minDelta + options.elipsis.length >= maxChars
) {
// If the slice is happening in the middle of a wide char, add one more char
const extraChar =
str.charCodeAt(maxChars - options.elipsis.length) > 255 ? 1 : 0;
str = str.slice(0, maxChars - options.elipsis.length + 1 + extraChar);
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if (options.breakOnWords) {
const ii = Math.max(str.lastIndexOf(' '), str.lastIndexOf('\n'));
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str = str.slice(0, ii);
}
str = str.trim() + options.elipsis;
}
return str;
};
module.exports = truncate;