The proposal “Numeric Separators” by Sam Goto and Rick Waldron lets us use _ as a separator in numeric literals. This blog post explains how that works. What are numeric literals? # JavaScript has several numeric literals: Decimal literals: 123.45, 86, 12e-5 Binary integer literals: 0b1011 Octal integer literals: 0o765 Hexadecimal integer literals: 0x2FF Interestingly, unary minus (-) is an opera