Didion was a typist, and a famous one. She kept notebooks for fragments and overheard lines, but the real work, the drafting and the endless reworking, happened at a keyboard. She even learned to type by copying out a master.

The Direct Answer
She typed her work, drafts and revisions alike.
She taught herself to type as a teenager by copying out Hemingway's stories, per her Paris Review interview.

Learning to Type on Hemingway

When Didion was fifteen or sixteen, she'd type out Hemingway's stories to learn how the sentences worked. She taught herself to type at the same time. Two skills, one habit. She wanted to feel the machinery of those clean, direct sentences under her own fingers, and the typewriter was how she did it. Years later she could still quote the feeling: very direct sentences, smooth rivers, clear water over granite, no sinkholes.

That early discipline stuck. Describing how long Play It As It Lays took, she called the real work sitting down at the typewriter and working every day until it was finished. The typewriter wasn't a prop. It was where the writing got made and remade.

When I was fifteen or sixteen I would type out his stories to learn how the sentences worked. I taught myself to type at the same time.

Joan Didion, The Paris Review, 1978

Notebooks, Then the Machine

Didion did write by hand, just not for the drafting. She carried a notebook for fragments, observations, and lines she overheard, the raw material she wrote about in Slouching Towards Bethlehem. As a traveling journalist and Vogue editor she famously hauled a Royal KMM typewriter everywhere, and her packing list in The White Album included a typewriter so she could sit down and start typing the day's notes wherever she landed.

Her tools changed over time. She moved through manual typewriters to electric, then to a computer by the late 1980s. The constant was the keyboard. To see how that fit her wider habits, read the full Joan Didion writing routine.

What You Can Steal