Javascript DataView Element Type

Introduction

The DataView makes no assumptions about what data type is stored inside the buffer.

We must specify an ElementType when reading or writing.

DataView will perform the conversion to execute that read or write.

Javascript 6 supports eight different ElementTypes:

Elementtype Bytes Description C EquivalentRange Of Values
Int81 8-bit signed integer signed char -128 to 127
Uint8 1 8-bit unsigned integer unsigned char 0 to 255
Int16 2 16-bit signed integershort -32768 to 32767
Uint16 2 16-bit unsigned integer unsigned short 0 to 65535
Int32 4 32-bit signed integerint -2,147,483,648 to 2,147,483,647
Uint32 4 32-bit unsigned integerunsigned int0 to 4,294,967,295
Float32 4 32-bit IEEE-754 floating point float -3.4E+38 to +3.4E+38
Float64 8 64-bit IEEE-754 floating point double -1.7E+308 to +1.7E+308

The DataView exposes get and set methods for each of these types.

It uses a byteOffset to address the buffer for reading and writing values. 

// Allocate two bytes of memory and declare a DataView 
const buf = new ArrayBuffer(2);//w w w  . j ava 2  s  .  c o m
const view = new DataView(buf);

console.log(view.getInt8(0)); // 0 
console.log(view.getInt8(1)); // 0 
console.log(view.getInt16(0)); // Check the entire buffer  

// Set the entire buffer to ones 255 in binary is 11111111 (2^8 - 1) 
view.setUint8(0, 255);
// DataView casts values to the designated Element Type, 255 in hex is 0xFF 
view.setUint8(1, 0xFF);

// read as a two's complement signed integer should be -1 
console.log(view.getInt16(0)); // -1



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