val.h (under-construction)¶

The Embind C++ class emscripten::val (defined in val.h) is used to transliterate JavaScript code to C++.

Guide material for this class can be found in Using val to transliterate JavaScript to C++.

class emscripten::val¶

This class is a C++ data type that can be used to represent (and provide convenient access to) any JavaScript object. You can use it to call a JavaScript object, read and write its properties, or coerce it to a C++ value like a bool, int, or std::string.

For example, the code below shows some simple JavaScript for making an XHR request on a URL:

var xhr = new XMLHttpRequest;
xhr.open("GET", "http://url");

This same code can be written in C++, using global() to get the symbol for the global XMLHttpRequest object and then using it to open a URL.

val xhr = val::global("XMLHttpRequest").new_();
xhr.call("open", std::string("GET"), std::string("http://url"));

See Using val to transliterate JavaScript to C++ for other examples.

static val array()¶

Creates and returns a new Array.

Returns:	The new Array.

static val object()¶

Creates and returns a new Object.

Returns:	The new Object.

static val undefined()¶

Creates a val that represents undefined.

Returns:	The val that represents undefined.

static val null()¶

Creates a val that represents null. val::undefined() is the same, but for undefined.

Returns:	A val that represents null.

static val take_ownership(internal::EM_VAL e)¶

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static val global(const char* name)¶

Looks up a global symbol.

Parameters const char* name:
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static val module_property(const char* name)¶

Looks up a symbol on the emscripten Module object.

Parameters const char* name:
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static val module_property(const char* name)

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explicit val(T&& value)¶

Constructor.

A val can be constructed by explicit construction from any C++ type. For example, val(true) or val(std::string("foo")).

Parameters T&& value:
	Any C++ type.

HamishW Don’t know how following “floating statement works”. Leaving here for discussion val() = delete;

explicit val(const char* v)¶

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Parameters const char* v:
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val(val&& v)¶

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Parameters val&& v:
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val(const val& v)¶

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Parameters const val& v:
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~val()¶

Destructor. HamishW-Replace with further description or delete comment.

val(const val& v)

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Parameters const val& v:
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val& operator=(val&& v)¶

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Parameters val&& v:
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val& operator=(const val& v)¶

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bool hasOwnProperty(const char* key) const¶

Test whether ... HamishW-Replace with description.

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val new_()¶

prototype:

template<typename... Args>
val new_(Args&&... args) const

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Parameters Args&&... args:
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val operator[](const T& key) const¶

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Parameters const T& key:
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void set(const K& key, const val& v)¶

Set the specified (key) property of a JavaScript object (accessed through a val) with the value v. HamishW-Replace with description.

Parameters:	const K& key – HamishW-Replace with description. Note that this is a templated value. const val& v – HamishW-Replace with description. Note that this is a templated value.

val operator()(Args&&... args)

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Parameters Args&&... args:
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ReturnValue call(const char* name, Args&&... args) const

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T as() const¶

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val typeof() const¶

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std::vector<T> vecFromJSArray(val v)¶

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Parameters val v:
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