How to encode base64 in an Azure Devops Pipelines extension

Question

I'm developing an Azure Pipelines extension in Typescript following their documentation

At some point I need to encode base64 a string. I tried using the btoa() function but the pipeline fails -> ##[error]btoa is not defined

async function run() {
    try {

    const someString = "xxx"
   
    //Encode Base64 someString
    const sonarqubeTokenBase64 = btoa(`${someString}:`)

    } catch (err) {
        tl.setResult(tl.TaskResult.Failed, err.message);
    }
}

How can I encode a string in this extension?