WebAssembly - Working with C

In this chapter, we are going to compile a simple C program to javascript and execute the same in the browser.

For Example − C Program

int square(int n) { 
   return n*n; 

We have done the installation of emsdk in folder wa/. In same folder, create another folder cprog/ and save above code as square.c.

We have already installed emsdk in the previous chapter. Here, we are going to make use of emsdk to compile the above c code.

Compile test.c in your command prompt as shown below −

emcc square.c -s STANDALONE_WASM –o findsquare.wasm

emcc command takes care of compiling the code as well as give you the .wasm code. We have used STANDALONE_WASM option that will give only the .wasm file.

Example − findsquare.html

<!doctype html> 
      <meta charset="utf-8">
      <title>WebAssembly Square function</title>
         div { 
            font-size : 30px; text-align : center; color:orange; 
      <div id="textcontent"></div>
      let square; fetch("findsquare.wasm").then(bytes => bytes.arrayBuffer()) 
      .then(mod => WebAssembly.compile(mod)) .then(module => {
         return new WebAssembly.Instance(module) 
      .then(instance => {
         square = instance.exports.square(13); 
         console.log("The square of 13 = " +square);         
         document.getElementById("textcontent").innerHTML = "The square of 13 = " +square; 


The output is as mentioned below −

Find Square HTML