JSExpr

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This package provides the @js macro which translates a Julia expression to JavaScript.

Example

julia> using JSExpr

julia> @js document.querySelector("#root")
WebIO.JSString("document.querySelector(\"#root\")")

julia> @js (a,b) -> a+b
WebIO.JSString("(function (a,b){return (a+b)})")

The JSString object wraps a Julia string. You can access the plain string from the .s field.

Interpolation

You can interpolate Julia objects or JSString expressions (i.e. result of @js macro invocations) in a @js macrocall.

julia> foo = 42
42

julia> callback = @js a -> a + $foo
WebIO.JSString("(function (a){return (a+42)})")

julia> f = @js array -> array.map($callback)
WebIO.JSString("(function (array){return array.map((function (a){return (a+42)}))})")

Converting a JSString or an object containing it to JSON serializes JSString as a string.

julia> JSON.print(Dict("foo" => "bar", "bar"=>f))
{"bar":"(function (array){return array.map((function (a){return (a+42)}))})","foo":"bar"}

This is not ideal when you want to use the serialized output as JavaScript, for example in a <script> tag. In this case, you should use JSExpr.jsexpr

julia> @js $(Dict("foo" => "bar", "bar"=>f))
WebIO.JSString("{\"bar\":(function (array){return array.map((function (a){return (a+42)}))}),\"foo\":\"bar\"}")

Object literals

The @js equivalent of

{foo: 42, bar: "baz"}

is

julia> @js d(foo=42, bar="baz")
WebIO.JSString("{foo:42,bar:\"baz\"}")

or a Dict

julia> @js Dict(:foo=>42, :bar=>"baz")
WebIO.JSString("{foo:42,bar:\"baz\"}")

Supported expressions

• Function call
• Comparison operators
• Dictionary / object literal
• Anonymous functions (automatically return the result)
• Function expressions (ditto)
• Assignment, = and +=, -=, *=, &=, |=
• If statements (@var expressions are not allowed in if statements yet). Note: if expressions are lowered to the ternary operator and hence return a value - this allows them to be used as the last expression in a function.
• Array indexing
• for expression on range literals (i.e. for x in a:b or for x in a:s:b)
• return statements
• @new Foo() as the equivalent of new Foo() in JS
• @var foo = bar as the equivalent of var foo = bar in JS