aa.js

class AudioBuffer {
  @TestAPI.props.readonly()
  duration() {
    return this.length / this.sampleRate;
  }
  
  @TestAPI.methods.param("destination", Float32Array)
  @TestAPI.methods.param("channelNumber", "positive number")
  @TestAPI.methods.param("[ startInChannel ]", "positive number")
  @TestAPI.methods.contract({
    precondition(destination, channelNumber, startInChannel = 0) {
      if (this._.length <= startInChannel) {
        throw new TypeError(``);
      }
    }
  })
  @TestAPI.versions({ chrome: "43-", firefox: "27-", safari: "none" })
  copyFromChannel(destination, channelNumber, startInChannel = 0) {
    /* ... */
  }
}