index.js
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'use strict';
const valueParser = require('postcss-value-parser');
/** @type {(node: valueParser.Node) => number} */
const getValue = (node) => parseFloat(node.value);
/* Works because toString() normalizes the formatting,
so comparing the string forms behaves the same as number equality*/
const conversions = new Map([
[[0.25, 0.1, 0.25, 1].toString(), 'ease'],
[[0, 0, 1, 1].toString(), 'linear'],
[[0.42, 0, 1, 1].toString(), 'ease-in'],
[[0, 0, 0.58, 1].toString(), 'ease-out'],
[[0.42, 0, 0.58, 1].toString(), 'ease-in-out'],
]);
/**
* @param {valueParser.Node} node
* @return {void | false}
*/
function reduce(node) {
if (node.type !== 'function') {
return false;
}
if (!node.value) {
return;
}
const lowerCasedValue = node.value.toLowerCase();
if (lowerCasedValue === 'steps') {
// Don't bother checking the step-end case as it has the same length
// as steps(1)
if (
node.nodes[0].type === 'word' &&
getValue(node.nodes[0]) === 1 &&
node.nodes[2] &&
node.nodes[2].type === 'word' &&
(node.nodes[2].value.toLowerCase() === 'start' ||
node.nodes[2].value.toLowerCase() === 'jump-start')
) {
/** @type string */ (node.type) = 'word';
node.value = 'step-start';
delete (/** @type Partial<valueParser.FunctionNode> */ (node).nodes);
return;
}
if (
node.nodes[0].type === 'word' &&
getValue(node.nodes[0]) === 1 &&
node.nodes[2] &&
node.nodes[2].type === 'word' &&
(node.nodes[2].value.toLowerCase() === 'end' ||
node.nodes[2].value.toLowerCase() === 'jump-end')
) {
/** @type string */ (node.type) = 'word';
node.value = 'step-end';
delete (/** @type Partial<valueParser.FunctionNode> */ (node).nodes);
return;
}
// The end case is actually the browser default, so it isn't required.
if (
node.nodes[2] &&
node.nodes[2].type === 'word' &&
(node.nodes[2].value.toLowerCase() === 'end' ||
node.nodes[2].value.toLowerCase() === 'jump-end')
) {
node.nodes = [node.nodes[0]];
return;
}
return false;
}
if (lowerCasedValue === 'cubic-bezier') {
const values = node.nodes
.filter((list, index) => {
return index % 2 === 0;
})
.map(getValue);
if (values.length !== 4) {
return;
}
const match = conversions.get(values.toString());
if (match) {
/** @type string */ (node.type) = 'word';
node.value = match;
delete (/** @type Partial<valueParser.FunctionNode> */ (node).nodes);
return;
}
}
}
/**
* @param {string} value
* @return {string}
*/
function transform(value) {
return valueParser(value).walk(reduce).toString();
}
/**
* @type {import('postcss').PluginCreator<void>}
* @return {import('postcss').Plugin}
*/
function pluginCreator() {
return {
postcssPlugin: 'postcss-normalize-timing-functions',
OnceExit(css) {
const cache = new Map();
css.walkDecls(
/^(-\w+-)?(animation|transition)(-timing-function)?$/i,
(decl) => {
const value = decl.value;
if (cache.has(value)) {
decl.value = cache.get(value);
return;
}
const result = transform(value);
decl.value = result;
cache.set(value, result);
}
);
},
};
}
pluginCreator.postcss = true;
module.exports = pluginCreator;