Check the manifest txt file in your addon folder and use the directives
Code:
##DependsOn
##OptionalDependsOn
put each addon name behind the directive line, with a splitting space, to assure that these addon names/library names get loaded BEFORE your addon's ON_LOAD event gets started.
e.g.
Code:
## OptionalDependsOn: libFilters-2.0 LibAddonMenu-2.0 ResearchAssistant SousChef VotansSettingsMenu PotionMaker CraftedPotions ChatMerchant InventoryGridView CraftBagExtended SetTracker AdvancedDisableControllerUI DetailedResearchScrolls
Inside your OnLoad event callback function you are able to check the addonName == "Other addon name" or if a global variable of the other addon exists you can check this by using something like
Lua Code:
--Is the addon "abc" is loaded yet?
if ABC ~= nil and ABC.functioName ~= nil then
--Addon abc is loaded and function functioName exists.
--Call the function now
ABC.functionName()
end