You can also apply a mixin globally. Use caution! Once you apply a mixin globally, it will affect every Vue instance created afterwards. When used properly, this can be used to inject processing logic for custom options:
Use global mixins sparsely and carefully, because it affects every single Vue instance created, including third party components. In most cases, you should only use it for custom option handling like demonstrated in the example above.
Custom Option Merge Strategies
When custom options are merged, they use the default strategy, which simply overwrites the existing value. If you want a custom option to be merged using custom logic, you need to attach a function to Vue.config.optionMergeStrategies:
For most object-based options, you can simply use the same strategy used by methods:
Mixins are a flexible way to distribute reusable functionalities for Vue components. A mixin object can contain any component options. When a component uses a mixin, all options in the mixin will be “mixed” into the component’s own options.
When a mixin and the component itself contain overlapping options, they will be “merged” using appropriate strategies. For example, hook functions with the same name are merged into an array so that all of them will be called. In addition, mixin hooks will be called before the component’s own hooks:
Options that expect object values, for example methods, components and directives, will be merged into the same object. The component’s options will take priority when there are conflicting keys in these objects:
Note that the same merge strategies are used in Vue.extend()