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minor improvement to string optimisation (#1514)

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- "" + "a"     => "a"
- "" + a + "b" => a + "b"
- "a" + ""     => "a" (improving on #45)
This commit is contained in:
Alex Lam S.L
2017-03-02 11:31:39 +08:00
committed by GitHub
parent 40ceddb48a
commit fdc9b9413b
2 changed files with 69 additions and 10 deletions
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29
lib/compress.js
View File

@@ -1054,12 +1054,6 @@ merge(Compressor.prototype, {
def(AST_Conditional, function(compressor){
return this.consequent.is_string(compressor) && this.alternative.is_string(compressor);
});
def(AST_Call, function(compressor){
return compressor.option("unsafe")
&& this.expression instanceof AST_SymbolRef
&& this.expression.name == "String"
&& this.expression.undeclared();
});
})(function(node, func){
node.DEFMETHOD("is_string", func);
});
@@ -2985,10 +2979,25 @@ merge(Compressor.prototype, {
}
}
}
if (self.operator == "+" && self.right instanceof AST_String
&& self.right.getValue() === "" && self.left instanceof AST_Binary
&& self.left.operator == "+" && self.left.is_string(compressor)) {
return self.left;
if (self.operator == "+") {
if (self.right instanceof AST_String
&& self.right.getValue() == ""
&& self.left.is_string(compressor)) {
return self.left;
}
if (self.left instanceof AST_String
&& self.left.getValue() == ""
&& self.right.is_string(compressor)) {
return self.right;
}
if (self.left instanceof AST_Binary
&& self.left.operator == "+"
&& self.left.left instanceof AST_String
&& self.left.left.getValue() == ""
&& self.right.is_string(compressor)) {
self.left = self.left.right;
return self.transform(compressor);
}
}
if (compressor.option("evaluate")) {
switch (self.operator) {

50
test/compress/concat-strings.js
View File

@@ -164,3 +164,53 @@ concat_6: {
);
}
}
concat_7: {
input: {
console.log(
"" + 1,
"" + "1",
"" + 1 + 2,
"" + 1 + "2",
"" + "1" + 2,
"" + "1" + "2",
"" + (x += "foo")
);
}
expect: {
console.log(
"" + 1,
"1",
"" + 1 + 2,
1 + "2",
"1" + 2,
"1" + "2",
x += "foo"
);
}
}
concat_8: {
input: {
console.log(
1 + "",
"1" + "",
1 + 2 + "",
1 + "2" + "",
"1" + 2 + "",
"1" + "2" + "",
(x += "foo") + ""
);
}
expect: {
console.log(
1 + "",
"1",
1 + 2 + "",
1 + "2",
"1" + 2,
"1" + "2",
x += "foo"
);
}
}