delaying nvm load until first usage in session

nvm_loader1.sh

#!/bin/bash

export NVM_DIR="$HOME/.nvm"

[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  # This loads nvm
[ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"  # This loads nvm bash_completion

-----
$ time source ./nvm_loader1.sh 

real    0m0.889s
user    0m0.668s
sys     0m0.317s

$ time nvm --version
0.33.8

real    0m0.007s
user    0m0.005s
sys     0m0.003s

$ time nvm --version
0.33.8

real    0m0.009s
user    0m0.010s
sys     0m0.000s

nvm_loader2.sh

#!/bin/bash

export NVM_DIR="$HOME/.nvm"

loadnvm() {
  unset -f npm npx node
  [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  # This loads nvm                                                  
  [ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"  # This loads nvm bash_completion                
  $@
}

nvm() { loadnvm nvm $@; }
npm() { loadnvm npm $@; }
npx() { loadnvm npx $@; }
node() { loadnvm node $@; }


-----
$ time source ./nvm_loader2.sh 

real    0m0.004s
user    0m0.004s
sys     0m0.000s

$ time nvm --version
0.33.8

real    0m0.866s
user    0m0.643s
sys     0m0.283s

$ time nvm --version
0.33.8

real    0m0.008s
user    0m0.007s
sys     0m0.003s