code: function normalize(arr) {
      const n = copy(arr);
      let len = 0;
      for (const v of n) len += v * v;
      if (len > 0) {
          const coeff = 1 / Math.sqrt(len);
          for (let k = 0; k < n.length; k++) {
              n[k] *= coeff;
          }
      }
      return n;
  }
docs: Make a vector have a length of 1.
  
  @param   {Float32Array} arr - Input vector.
  @returns {Float32Array} A new vector.