77 lines
2.1 KiB
JavaScript
77 lines
2.1 KiB
JavaScript
var t = require("../../../types");
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exports.optional = true;
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exports.ExpressionStatement = function (node) {
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// remove consequenceless expressions such as local variables and literals
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//
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// var foo = true; foo; -> var foo = true;
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// "foo"; ->
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//
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var expr = node.expression;
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if (t.isLiteral(expr) || (t.isIdentifier(node) && t.hasBinding(node.name))) {
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this.remove();
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}
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};
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exports.IfStatement = {
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exit: function (node) {
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// todo: in scenarios where we can just return the consequent or
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// alternate we should drop the block statement if it contains no
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// block scoped variables
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var consequent = node.consequent;
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var alternate = node.alternate;
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var test = node.test;
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// we can check if a test will be truthy 100% and if so then we can inline
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// the consequent and completely ignore the alternate
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//
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// if (true) { foo; } -> { foo; }
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// if ("foo") { foo; } -> { foo; }
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//
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if (t.isLiteral(test) && test.value) {
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return alternate;
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}
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// we can check if a test will be falsy 100% and if so we can inline the
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// alternate if there is one and completely remove the consequent
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//
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// if ("") { bar; } else { foo; } -> { foo; }
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// if ("") { bar; } ->
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//
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if (t.isFalsyExpression(test)) {
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if (alternate) {
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return alternate;
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} else {
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return this.remove();
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}
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}
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// remove alternate blocks that are empty
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//
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// if (foo) { foo; } else {} -> if (foo) { foo; }
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//
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if (t.isBlockStatement(alternate) && !alternate.body.length) {
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alternate = node.alternate = null;
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}
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// if the consequent block is empty turn alternate blocks into a consequent
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// and flip the test
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//
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// if (foo) {} else { bar; } -> if (!foo) { bar; }
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//
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if (t.blockStatement(consequent) && !consequent.body.length &&
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t.isBlockStatement(alternate) && alternate.body.length) {
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node.consequent = node.alternate;
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node.alternate = null;
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node.test = t.unaryExpression("!", test, true);
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}
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}
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};
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