Basic concepts

o1js is a TypeScript (TS) library for writing general-purpose zero knowledge (zk) programs and writing zk smart contracts for Mina.

Field

Field elements are the basic unit of data in zero knowledge proof programming. Each field element can store a number up to almost 256 bits in size. You can think of a field element as a uint256 in Solidity.

For example, in typical programming, you might use:

const sum = 1 + 3

In o1js, you write this as:

const sum = new Field(1).add(new Field(3))

This can be simplified as:

const sum = new Field(1).add(3)

Note that the 3 is auto-promoted to a field type to make this cleaner.

Built-in data types

Some common data types you may use are:

new Bool(x);   // accepts true or false
new Field(x);  // accepts an integer, or a numeric string if you want to represent a number greater than JavaScript can represent but within the max value that a field can store.
new UInt64(x); // accepts a Field - useful for constraining numbers to 64 bits
new UInt32(x); // accepts a Field - useful for constraining numbers to 32 bits

In the case of Field and Bool, you can also call the constructor without new:

const x = Field(10);
const b = Bool(true);

Try out different types

Create a variable sum for a Field which adds 3 to the Field which has a value of 1:

const sum = Field(1).add(3);

Create a variable bool for a Bool which accepts true or false

const bool = Bool(true);

Create a variable int32 for a UInt32 which accepts a Field - useful for constraining numbers to 32 bits

const int32 = new UInt32(123);

Create a variable int64 for a UInt64 which accepts a Field - useful for constraining numbers to 64 bits

const int64 = new UInt64(1234);

Add log statements for the variables: sum, bool, int32, int64 so you can see the underlying values:

Provable.log("sum has the value:", sum);
Provable.log("bool has the value:", bool);
Provable.log("int32 has the value:", int32);
Provable.log("int64 has the value", int64);

Now build and run the script in the terminal:

npm run build && node build/src/index.js