Instructions and Data Types

In this guide, we’ll dive into WebAssembly’s core instructions (the verbs) and data types (the nouns) that power efficient, predictable execution in browsers and other WASM runtimes. By mastering these fundamentals, you can write low-level modules that perform reliably across platforms.

WebAssembly Instructions

WebAssembly instructions are low-level opcodes executed by the WASM virtual machine. Because they resemble machine code more than high-level languages, browsers can optimize them aggressively for speed.

Basic Arithmetic Examples

i32.add ‒ adds two 32-bit integers
f64.sub ‒ subtracts one 64-bit float from another

i32.add    ;; adds two i32 values
f64.sub    ;; subtracts one f64 value from another

Each instruction strictly enforces its operand types. Supplying mismatched types (e.g., passing a boolean into an arithmetic opcode) will trigger a runtime trap.

Always verify operand types before invoking an instruction. WebAssembly performs no implicit conversions and will trap on type mismatches.

WebAssembly Data Types

Choosing the right data type in WebAssembly ensures efficient memory usage and accurate calculations. For instance, consider a web app that displays two temperature readings:

25 °C (an integer)
25.5 °C (a decimal)

In WASM you’d represent these as:

25 °C → i32
25.5 °C → f64

The image illustrates WebAssembly data types, showing temperature values (25°C and 25.5°C) alongside a code snippet with "i32" and "f64" data types.

Below is a quick overview of the core WebAssembly types:

Data Type	Size & Kind	Use Case
`i32`	32-bit integer	Counters, array indices
`i64`	64-bit integer	High-precision integer math
`f32`	32-bit floating point	Graphics, simple physics
`f64`	64-bit floating point	Scientific calculations, audio DSP
`v128`	128-bit SIMD vector	Parallel data processing
`funcref`	Reference to a function	Indirect calls, function tables
`externref`	Reference to external value	Interop with host (e.g., JavaScript)

The image is a diagram showing WebAssembly data types, categorized into integers (i32, i64), floating-point numbers (f32, f64), and others (v128, funcref, externref).

Fundamental WebAssembly Instructions

WebAssembly categorizes its instructions into arithmetic, comparison, control flow, and memory operations. Here’s a concise reference:

;; Arithmetic
i32.add      ;; add two 32-bit integers
i64.sub      ;; subtract two 64-bit integers
f32.mul      ;; multiply two 32-bit floats
f64.div      ;; divide two 64-bit floats

;; Comparison
i32.eq       ;; equal? (32-bit integers)
f64.ne       ;; not equal? (64-bit floats)
i32.lt_s     ;; less than (signed 32-bit integers)
f32.ge       ;; greater than or equal (32-bit floats)

;; Control Flow
block        ;; start a block
loop         ;; start a loop
if           ;; conditional branch
br           ;; branch to a label

;; Memory
i32.load     ;; load a 32-bit integer from memory
f64.store    ;; store a 64-bit float to memory
memory.size  ;; query current memory pages
memory.grow  ;; expand memory by pages

Introduction

Introduction to WebAssembly (WASM)

WebAssembly Core Concepts

Getting Started with WebAssembly

Compiling to WebAssembly

Future: WebAssembly in Cloud

Community & Resources

Instructions and Data Types

WebAssembly Instructions

Basic Arithmetic Examples

WebAssembly Data Types

Fundamental WebAssembly Instructions

Further Reading

Watch Video

​WebAssembly Instructions

​Basic Arithmetic Examples

​WebAssembly Data Types

​Fundamental WebAssembly Instructions

​Further Reading

Watch Video

WebAssembly Instructions

Basic Arithmetic Examples

WebAssembly Data Types

Fundamental WebAssembly Instructions

Further Reading