"Jerry's Diary" is the first "cheater" in the "Tom and Jerry" series. To save money on animation, studios sometimes made short subjects that employed clips from older cartoons. In this case, the plot involves Tom reading Jerry's diary, which allows for flashbacks, each of which is really a clip of an earlier short.
In the postwar years, radio was still the mainstay of home entertainment, as television was in its early stages of roll out. Shorts like this, which were shown in cinemas as part of a program, featured careful attention to detail---including all the very latest furnishings and accessories, especially modern kitchens. Even a simple table leg or a baseboard was meticulously drawn by the animators
Tom is in his early incarnation here, with a light patch of fur between his eyes. He also is drawn more like an actual house cat.
Tom is heard laughing here several times. He's usually the silent type.
The metal grated wall fixture near Jerry's mouse-hole was actually a vent that provides heating to the home, usually from a furnace or boiler down in the cellar.