$ gcc spectre.c -o spectre
$ ./spectre 16 6
Reading 6 bytes at 16:
offset=16 byte=102 0x66 'f'
offset=17 byte=111 0x6f 'o'
offset=18 byte=111 0x6f 'o'
offset=19 byte=98 0x62 'b'
offset=20 byte=97 0x61 'a'
offset=21 byte=114 0x72 'r'

Enable #shared-array-buffer in chrome:///flags under your own risk...

Extracted from: http://xlab.tencent.com/special/spectre/spectre_check.html

Less reliable (no majority vote, less tries) but slightly simplified for my own understanding.

In order to make a real "out-of-bounds" read, vul_call should be a native JS array boundary check and the length field should be evicted before each test in order to create the window for speculative execution.

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