/
index.js
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/
index.js
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"use strict";
const evaluate = require("babel-helper-evaluate-path");
const { FALLBACK_HANDLER } = require("./replacements");
function getName(member) {
if (member.computed) {
switch (member.property.type) {
case "StringLiteral":
case "NumericLiteral":
return member.property.value;
case "TemplateLiteral":
return;
}
} else {
return member.property.name;
}
}
function swap(path, member, handlers, ...args) {
const key = getName(member.node);
if (key === void 0) return false;
let handler;
if (hop(handlers, key) && typeof handlers[key] === "function") {
handler = handlers[key];
} else if (typeof handlers[FALLBACK_HANDLER] === "function") {
handler = handlers[FALLBACK_HANDLER].bind(member.get("object"), key);
} else {
return false;
}
const replacement = handler.apply(member.get("object"), args);
if (replacement) {
path.replaceWith(replacement);
return true;
}
return false;
}
module.exports = babel => {
const replacements = require("./replacements.js")(babel);
const seen = Symbol("seen");
const { types: t } = babel;
return {
name: "minify-constant-folding",
visitor: {
// Evaluate string expressions that are next to each other
// but are not actually a binary expression.
// "a" + b + "c" + "d" -> "a" + b + "cd"
BinaryExpression(path) {
if (!path.isBinaryExpression({ operator: "+" })) {
return;
}
let literal, bin;
const left = path.get("left");
const right = path.get("right");
if (right.isStringLiteral()) {
literal = right;
if (left.isBinaryExpression({ operator: "+" })) {
bin = left;
} else {
return;
}
} else if (left.isStringLiteral()) {
literal = left;
if (right.isBinaryExpression({ operator: "+" })) {
bin = right;
} else {
return;
}
} else {
return;
}
const relevant = getLeaf(bin, literal.key);
if (!relevant) {
return;
}
const value =
literal.key === "right"
? relevant.node.value + literal.node.value
: literal.node.value + relevant.node.value;
relevant.replaceWith(t.stringLiteral(value));
path.replaceWith(bin.node);
function getLeaf(path, direction) {
if (path.isStringLiteral()) {
return path;
} else if (path.isBinaryExpression({ operator: "+" })) {
return getLeaf(path.get(direction), direction);
}
}
},
// TODO: look into evaluating binding too (could result in more code, but gzip?)
Expression(path, { opts: { tdz = false } = {} }) {
const { node, parent } = path;
if (node[seen]) {
return;
}
if (path.isLiteral()) {
return;
}
if (!path.isPure()) {
return;
}
// Avoid replacing the values for identifiers in exports
if (t.isExportSpecifier(parent)) {
return;
}
// -0 maybe compared via dividing and then checking against -Infinity
// Also -X will always be -X.
if (
t.isUnaryExpression(node, { operator: "-" }) &&
t.isNumericLiteral(node.argument)
) {
return;
}
// We have a transform that converts true/false to !0/!1
if (
t.isUnaryExpression(node, { operator: "!" }) &&
t.isNumericLiteral(node.argument)
) {
if (node.argument.value === 0 || node.argument.value === 1) {
return;
}
}
// void 0 is used for undefined.
if (
t.isUnaryExpression(node, { operator: "void" }) &&
t.isNumericLiteral(node.argument, { value: 0 })
) {
return;
}
const res = evaluate(path, { tdz });
if (res.confident) {
// Avoid fractions because they can be longer than the original expression.
// There is also issues with number precision?
if (typeof res.value === "number" && !Number.isInteger(res.value)) {
return;
}
// Preserve -0
if (typeof res.value === "number" && res.value === 0) {
if (1 / res.value === -Infinity) {
const node = t.unaryExpression("-", t.numericLiteral(0), true);
node[seen] = true;
path.replaceWith(node);
return;
}
}
// this will convert object to object but
// t.valueToNode has other effects where property name
// is not treated for the respective environment.
// So we bail here for objects and let other plugins
// take care of converting String literal to Identifier
if (typeof res.value === "object") {
return;
}
const node = t.valueToNode(res.value);
node[seen] = true;
path.replaceWith(node);
}
},
CallExpression(path) {
const { node } = path;
const member = path.get("callee");
if (t.isMemberExpression(member)) {
const helpers = replacements[member.node.object.type];
if (!helpers || !helpers.calls) return;
// find if the input can be constant folded
if (
typeof helpers.canReplace === "function" &&
!helpers.canReplace.call(member.get("object"))
) {
return;
}
swap(path, member, helpers.calls, ...node.arguments);
}
},
MemberExpression(path) {
const { node } = path;
const helpers = replacements[node.object.type];
if (!helpers || !helpers.members) return;
swap(path, path, helpers.members);
}
}
};
};
function hop(o, key) {
return Object.prototype.hasOwnProperty.call(o, key);
}