Sourced from terser's changelog.

v4.8.1 (backport)

• Security fix for RegExps that should not be evaluated (regexp DDOS)

v4.8.0

• Support for numeric separators (million = 1_000_000) was added.
• Assigning properties to a class is now assumed to be pure.
• Fixed bug where yield wasn't considered a valid property key in generators.

v4.7.0

• A bug was fixed where an arrow function would have the wrong size
• arguments object is now considered safe to retrieve properties from (useful for length, or 0) even when pure_getters is not set.
• Fixed erroneous const declarations without value (which is invalid) in some corner cases when using collapse_vars.

v4.6.13

• Fixed issue where ES5 object properties were being turned into ES6 object properties due to more lax unicode rules.
• Fixed parsing of BigInt with lowercase e in them.

v4.6.12

• Fixed subtree comparison code, making it see that [1,[2, 3]] is different from [1, 2, [3]]
• Printing of unicode identifiers has been improved

v4.6.11

• Read unused classes' properties and method keys, to figure out if they use other variables.
• Prevent inlining into block scopes when there are name collisions
• Functions are no longer inlined into parameter defaults, because they live in their own special scope.
• When inlining identity functions, take into account the fact they may be used to drop this in function calls.
• Nullish coalescing operator (x ?? y), plus basic optimization for it.
• Template literals in binary expressions such as + have been further optimized

v4.6.10

• Do not use reduce_vars when classes are present

v4.6.9

• Check if block scopes actually exist in blocks

v4.6.8

• Take into account "executed bits" of classes like static properties or computed keys, when checking if a class evaluation might throw or have side effects.

v4.6.7

• Some new performance gains through a AST_Node.size() method which measures a node's source code length without printing it to a string first.

... (truncated)

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