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101 lines
2.5 KiB
JavaScript
101 lines
2.5 KiB
JavaScript
'use strict'
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var acorn = require('acorn');
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var walk = require('acorn/dist/walk');
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var lastSRC = '(null)';
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var lastRes = true;
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var lastConstants = undefined;
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var STATEMENT_WHITE_LIST = {
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'EmptyStatement': true,
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'ExpressionStatement': true,
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};
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var EXPRESSION_WHITE_LIST = {
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'ParenthesizedExpression': true,
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'ArrayExpression': true,
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'ObjectExpression': true,
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'SequenceExpression': true,
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'TemplateLiteral': true,
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'UnaryExpression': true,
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'BinaryExpression': true,
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'LogicalExpression': true,
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'ConditionalExpression': true,
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'Identifier': true,
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'Literal': true,
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'ComprehensionExpression': true,
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'TaggedTemplateExpression': true,
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'MemberExpression': true,
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'CallExpression': true,
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'NewExpression': true,
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};
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module.exports = isConstant;
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function isConstant(src, constants) {
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src = '(' + src + ')';
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if (lastSRC === src && lastConstants === constants) return lastRes;
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lastSRC = src;
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lastConstants = constants;
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if (!isExpression(src)) return lastRes = false;
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var ast;
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try {
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ast = acorn.parse(src, {
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ecmaVersion: 6,
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allowReturnOutsideFunction: true,
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allowImportExportEverywhere: true,
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allowHashBang: true
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});
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} catch (ex) {
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return lastRes = false;
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}
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var isConstant = true;
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walk.simple(ast, {
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Statement: function (node) {
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if (isConstant) {
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if (STATEMENT_WHITE_LIST[node.type] !== true) {
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isConstant = false;
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}
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}
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},
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Expression: function (node) {
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if (isConstant) {
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if (EXPRESSION_WHITE_LIST[node.type] !== true) {
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isConstant = false;
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}
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}
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},
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MemberExpression: function (node) {
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if (isConstant) {
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if (node.computed) isConstant = false;
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else if (node.property.name[0] === '_') isConstant = false;
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}
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},
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Identifier: function (node) {
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if (isConstant) {
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if (!constants || !(node.name in constants)) {
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isConstant = false;
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}
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}
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},
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});
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return lastRes = isConstant;
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}
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isConstant.isConstant = isConstant;
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isConstant.toConstant = toConstant;
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function toConstant(src, constants) {
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if (!isConstant(src, constants)) throw new Error(JSON.stringify(src) + ' is not constant.');
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return Function(Object.keys(constants || {}).join(','), 'return (' + src + ')').apply(null, Object.keys(constants || {}).map(function (key) {
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return constants[key];
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}));
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}
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function isExpression(src) {
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try {
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eval('throw "STOP"; (function () { return (' + src + '); })()');
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return false;
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}
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catch (err) {
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return err === 'STOP';
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}
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}
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