goja-core/src/main/java/goja/core/kits/stream/FastCharBuffer.java
public CharSequence subSequence(int start, int end) {
        int len = end - start;
        return new StringBuilder(len).append(toArray(start, len));
    }
public CharSequence subSequence(int start, int end) {
        int len = end - start;
        return new StringBuilder(len).append(toArray(start, len));
    }
Returns sub sequence.