John Gill Commentary Genesis 21:6

"And Sarah said, God hath made me to laugh. Every one that heareth will laugh with me." — Genesis 21:6 (ASV)

And Sarah said, God has made me to laugh

This she said on occasion of the name of her son Isaac, which name her husband had given him by divine direction, and to which she assented. This doubtless brought to her mind her former laughing, when she first heard that she should have a son, which was in a way of diffidence and distrust; but now God having given her a son, laid a foundation for laughter of another kind, for real, solid, joy and thankfulness.

[so that] all that hear will laugh with me

Not laugh at her, and deride her, as Piscator interprets it; but congratulate her, and rejoice with her on this occasion, as on a like one the neighbours of Elisabeth did with her, (Luke 1:58) .