store: Wasm text instruction

The store memory instructions, are used to store a number on the stack in a memory.

There are store instructions for storing an i32, i64, f32, and f64 in memory. For the integer numbers, there are separate instruction variants for storing a wide typed number into a narrower number in memory. For example, you can store a 32-bit number into an 8-bit slot in memory using i32.store8. If the number doesn't fit in the narrower number type it will wrap. All the variants are listed below.

Try it

(module

  (memory $memory 1)
  (export "memory" (memory $memory))

  (func (export "store_in_mem") (param $num i32)
    i32.const 0
    local.get $num

    ;; store $num at position 0
    i32.store
  )

)
const url = "{%wasm-url%}";
const result = await WebAssembly.instantiateStreaming(fetch(url));

const store_in_mem = result.instance.exports.store_in_mem;
const memory = result.instance.exports.memory;

store_in_mem(100);

const dataView = new DataView(memory.buffer);
const first_number_in_mem = dataView.getUint32(0, true);

console.log(first_number_in_mem);
// Expected output: 100

Syntax

Store in default memory

wat
;; Store value in default memory at particular offset
i32.const 0 ;; stack variable with offset in memory to store the number
i32.const 20 ;; stack variable with the number to store
i32.store ;; store in default memory

;; Store using S-expression (same values and offset)
(i32.store (i32.const 0) (i32.const 20))

Store to specified memory (if multi-memory supported)

wat
;; Store in memory referenced by its index
i32.const 0 ;; offset in memory to store the number
i32.const 20 ;; the number to store
i32.store (memory 2)  ;; store in memory with index 2

;; Store in memory referenced by its name
i32.const 0 ;; offset to store the number
i32.const 20 ;; the number to store
i32.store (memory $memoryName)  ;; store in memory with name "$memoryName"

;; Store in same memory using an S-expression
(i32.store (memory $memoryName) (i32.const 0) (i32.const 20))

Instructions and opcodes

Instruction Binary opcode
i32.store 0x36
i64.store 0x37
f32.store 0x38
f64.store 0x39
i32.store8 0x3a
i32.store16 0x3b
i64.store8 0x3c
i64.store16 0x3d
i64.store32 0x3e

Specifications

Specification
Unknown specification
# syntax-instr-memory

Browser compatibility

webassembly.api.Memory

desktop mobile server
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Bun
Deno
Node.js
Memory
Chrome – Full support
Chrome 57 (Release date: 2017-03-09)
footnote Full support
Edge – Full support
Edge 16 (Release date: 2017-10-17)
footnote Full support
Firefox – Full support
Firefox 52 (Release date: 2017-03-07)
footnote Full support
Opera – Full support
Opera 44 (Release date: 2017-03-21)
footnote Full support
Safari – Full support
Safari 11 (Release date: 2017-09-19)
footnote Full support
Chrome Android – Full support
Chrome Android 57 (Release date: 2017-03-16)
footnote Full support
Firefox for Android – Full support
Firefox for Android 52 (Release date: 2017-03-07)
footnote Full support
Opera Android – Full support
Opera Android 43 (Release date: 2017-09-27)
footnote Full support
Safari on iOS – Full support
Safari on iOS 11 (Release date: 2017-09-19)
footnote Full support
Samsung Internet – Full support
Samsung Internet 7 (Release date: 2018-03-16)
footnote Full support
WebView Android – Full support
WebView Android 57 (Release date: 2017-03-16)
footnote Full support
WebView on iOS – Full support
WebView on iOS 11 (Release date: 2017-09-19)
footnote Full support
Bun – Full support
Bun 1 (Release date: 2023-09-08)
footnote Full support
Deno – Full support
Deno 1 (Release date: 2020-05-13)
footnote Full support
Node.js – Full support
Node.js 8 (Release date: 2017-05-30)
footnote Full support
Memory() constructor
Chrome – Full support
Chrome 57 (Release date: 2017-03-09)
footnote Full support
Edge – Full support
Edge 16 (Release date: 2017-10-17)
footnote Full support
Firefox – Full support
Firefox 52 (Release date: 2017-03-07)
footnote Full support
Opera – Full support
Opera 44 (Release date: 2017-03-21)
footnote Full support
Safari – Full support
Safari 11 (Release date: 2017-09-19)
footnote Full support
Chrome Android – Full support
Chrome Android 57 (Release date: 2017-03-16)
footnote Full support
Firefox for Android – Full support
Firefox for Android 52 (Release date: 2017-03-07)
footnote Full support
Opera Android – Full support
Opera Android 43 (Release date: 2017-09-27)
footnote Full support
Safari on iOS – Full support
Safari on iOS 11 (Release date: 2017-09-19)
footnote Full support
Samsung Internet – Full support
Samsung Internet 7 (Release date: 2018-03-16)
footnote Full support
WebView Android – Full support
WebView Android 57 (Release date: 2017-03-16)
footnote Full support
WebView on iOS – Full support
WebView on iOS 11 (Release date: 2017-09-19)
footnote Full support
Bun – Full support
Bun 1 (Release date: 2023-09-08)
footnote Full support
Deno – Full support
Deno 1 (Release date: 2020-05-13)
footnote Full support
Node.js – Full support
Node.js 8 (Release date: 2017-05-30)
footnote Full support
shared flag
Chrome – Full support
Chrome 74 (Release date: 2019-04-23)
footnote Full support
Edge – Full support
Edge 79 (Release date: 2020-01-15)
footnote Full support
Firefox – Full support
Firefox 78 (Release date: 2020-06-30)
footnote Full support
Opera – Full support
Opera 62 (Release date: 2019-06-27)
footnote Full support
Safari – Full support
Safari 15.2 (Release date: 2021-12-13)
footnote
footnote Shared WebAssembly.Memory is gated behind COOP/COEP. For more detail, read Making your website "cross-origin isolated" using COOP and COEP.
Chrome Android – Full support
Chrome Android 88 (Release date: 2021-01-19)
footnote Full support
Firefox for Android – Full support
Firefox for Android 79 (Release date: 2020-07-28)
footnote Full support
Opera Android – Full support
Opera Android 63 (Release date: 2021-04-16)
footnote Full support
Safari on iOS – Full support
Safari on iOS 15.2 (Release date: 2021-12-13)
footnote
footnote Shared WebAssembly.Memory is gated behind COOP/COEP. For more detail, read Making your website "cross-origin isolated" using COOP and COEP.
Samsung Internet – Full support
Samsung Internet 15 (Release date: 2021-08-13)
footnote Full support
WebView Android – No support
WebView Android
footnote No support
WebView on iOS – Full support
WebView on iOS 15.2 (Release date: 2021-12-13)
footnote
footnote Shared WebAssembly.Memory is gated behind COOP/COEP. For more detail, read Making your website "cross-origin isolated" using COOP and COEP.
Bun – No support
Bun
footnote No support
Deno – Full support
Deno 1.10 (Release date: 2021-05-11)
footnote Full support
Node.js – Full support
Node.js 16.6 (Release date: 2021-07-29)
footnote Full support
buffer
Chrome – Full support
Chrome 57 (Release date: 2017-03-09)
footnote Full support
Edge – Full support
Edge 16 (Release date: 2017-10-17)
footnote Full support
Firefox – Full support
Firefox 52 (Release date: 2017-03-07)
footnote Full support
Opera – Full support
Opera 44 (Release date: 2017-03-21)
footnote Full support
Safari – Full support
Safari 11 (Release date: 2017-09-19)
footnote Full support
Chrome Android – Full support
Chrome Android 57 (Release date: 2017-03-16)
footnote Full support
Firefox for Android – Full support
Firefox for Android 52 (Release date: 2017-03-07)
footnote Full support
Opera Android – Full support
Opera Android 43 (Release date: 2017-09-27)
footnote Full support
Safari on iOS – Full support
Safari on iOS 11 (Release date: 2017-09-19)
footnote Full support
Samsung Internet – Full support
Samsung Internet 7 (Release date: 2018-03-16)
footnote Full support
WebView Android – Full support
WebView Android 57 (Release date: 2017-03-16)
footnote Full support
WebView on iOS – Full support
WebView on iOS 11 (Release date: 2017-09-19)
footnote Full support
Bun – Full support
Bun 1 (Release date: 2023-09-08)
footnote Full support
Deno – Full support
Deno 1 (Release date: 2020-05-13)
footnote Full support
Node.js – Full support
Node.js 8 (Release date: 2017-05-30)
footnote Full support
grow
Chrome – Full support
Chrome 57 (Release date: 2017-03-09)
footnote Full support
Edge – Full support
Edge 16 (Release date: 2017-10-17)
footnote Full support
Firefox – Full support
Firefox 52 (Release date: 2017-03-07)
footnote Full support
Opera – Full support
Opera 44 (Release date: 2017-03-21)
footnote Full support
Safari – Full support
Safari 11 (Release date: 2017-09-19)
footnote Full support
Chrome Android – Full support
Chrome Android 57 (Release date: 2017-03-16)
footnote Full support
Firefox for Android – Full support
Firefox for Android 52 (Release date: 2017-03-07)
footnote Full support
Opera Android – Full support
Opera Android 43 (Release date: 2017-09-27)
footnote Full support
Safari on iOS – Full support
Safari on iOS 11 (Release date: 2017-09-19)
footnote Full support
Samsung Internet – Full support
Samsung Internet 7 (Release date: 2018-03-16)
footnote Full support
WebView Android – Full support
WebView Android 57 (Release date: 2017-03-16)
footnote Full support
WebView on iOS – Full support
WebView on iOS 11 (Release date: 2017-09-19)
footnote Full support
Bun – Full support
Bun 1 (Release date: 2023-09-08)
footnote Full support
Deno – Full support
Deno 1 (Release date: 2020-05-13)
footnote Full support
Node.js – Full support
Node.js 8 (Release date: 2017-05-30)
footnote Full support
toFixedLengthBuffer
Chrome – Full support
Chrome 144 (Release date: 2026-01-13)
footnote Full support
Edge – Full support
Edge 144 (Release date: 2026-01-21)
footnote Full support
Firefox – Full support
Firefox 145 (Release date: 2025-11-11)
footnote Full support
Opera – Full support
Opera 128 (Release date: 2026-02-26)
footnote Full support
Safari – Full support
Safari 26.2 (Release date: 2025-12-12)
footnote Full support
Chrome Android – Full support
Chrome Android 144 (Release date: 2026-01-13)
footnote Full support
Firefox for Android – Full support
Firefox for Android 145 (Release date: 2025-11-11)
footnote Full support
Opera Android – Full support
Opera Android 95 (Release date: 2026-02-11)
footnote Full support
Safari on iOS – Full support
Safari on iOS 26.2 (Release date: 2025-12-12)
footnote Full support
Samsung Internet – No support
Samsung Internet
footnote No support
WebView Android – Full support
WebView Android 144 (Release date: 2026-01-13)
footnote Full support
WebView on iOS – Full support
WebView on iOS 26.2 (Release date: 2025-12-12)
footnote Full support
Bun – No support
Bun
footnote No support
Deno – No support
Deno
footnote No support
Node.js – No support
Node.js
footnote No support
toResizableBuffer
Chrome – Full support
Chrome 144 (Release date: 2026-01-13)
footnote Full support
Edge – Full support
Edge 144 (Release date: 2026-01-21)
footnote Full support
Firefox – Full support
Firefox 145 (Release date: 2025-11-11)
footnote Full support
Opera – Full support
Opera 128 (Release date: 2026-02-26)
footnote Full support
Safari – Full support
Safari 26.2 (Release date: 2025-12-12)
footnote Full support
Chrome Android – Full support
Chrome Android 144 (Release date: 2026-01-13)
footnote Full support
Firefox for Android – Full support
Firefox for Android 145 (Release date: 2025-11-11)
footnote Full support
Opera Android – Full support
Opera Android 95 (Release date: 2026-02-11)
footnote Full support
Safari on iOS – Full support
Safari on iOS 26.2 (Release date: 2025-12-12)
footnote Full support
Samsung Internet – No support
Samsung Internet
footnote No support
WebView Android – Full support
WebView Android 144 (Release date: 2026-01-13)
footnote Full support
WebView on iOS – Full support
WebView on iOS 26.2 (Release date: 2025-12-12)
footnote Full support
Bun – No support
Bun
footnote No support
Deno – No support
Deno
footnote No support
Node.js – No support
Node.js
footnote No support

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
No support
No support
See implementation notes.

webassembly.multiMemory

desktop mobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
multiMemory
Chrome – Full support
Chrome 120 (Release date: 2023-12-05)
footnote Full support
Edge – Full support
Edge 120 (Release date: 2023-12-07)
footnote Full support
Firefox – Full support
Firefox 125 (Release date: 2024-04-16)
footnote Full support
Opera – Full support
Opera 106 (Release date: 2023-12-19)
footnote Full support
Safari – No support
Safari
footnote No support
Chrome Android – Full support
Chrome Android 120 (Release date: 2023-12-05)
footnote Full support
Firefox for Android – Full support
Firefox for Android 125 (Release date: 2024-04-16)
footnote Full support
Opera Android – Full support
Opera Android 80 (Release date: 2024-01-25)
footnote Full support
Safari on iOS – No support
Safari on iOS
footnote No support
Samsung Internet – Full support
Samsung Internet 25 (Release date: 2024-04-24)
footnote Full support
WebView Android – Full support
WebView Android 120 (Release date: 2023-12-05)
footnote Full support
WebView on iOS – No support
WebView on iOS
footnote No support

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
No support
No support

Note: The multiMemory compatibility table indicates versions in which store can be used with a specified memory.